A land drilling rig is a set of systems that work together. One lifts and lowers the drill string, one turns it, one pumps drilling fluid through it, one powers everything, and one controls pressure at the wellhead. When you buy a rig, or a single component to complete one, each of those systems comes with its own spec sheet and its own paper trail.
Most rig diagrams stop at what each part does. This guide adds the buyer's side. For each of 13 major components it lists the specs people actually line up between listings, and the documents worth requesting before anything is signed. It follows the order in which a rig package is usually described in a listing: system by system.
Select a numbered marker on the drawing, or a part name in the list under it. The details open beside the drawing on a large screen and under it on a phone. Every entry is also written out in full further down the page, so you can read straight through instead.
Hoisting system
The hoisting system raises and lowers everything that goes into the hole: drill pipe, casing and downhole tools. Its main parts are the mast and substructure that carry the load, the crown and traveling blocks that multiply the pull of the drilling line, and the drawworks that reels the line in and out.
When buyers compare two rigs of the same horsepower class, hoisting specs are usually the first numbers they set side by side, because they decide which wells a rig can drill and how quickly it can move pipe.
1 · Hoisting system
Mast and substructure
What it does
The mast is the tall steel structure that holds the crown block above the rig floor and gives the crew room to stand pipe upright. The substructure is the base it stands on. It raises the rig floor high enough to fit the wellhead equipment underneath, and it carries the weight of the pipe stood back on the floor.
Many modern land rigs use a mast that is raised and lowered in one piece, and a substructure that lifts itself to working height after the rig is assembled. Pad rigs add a skidding or walking system so the whole rig can move between wells without being taken apart.
Specs buyers compare
- Mast type (cantilever, telescoping or a fixed derrick) and how it is raised
- Clear height, and whether it is built to rack doubles or triples (two- or three-joint stands of pipe)
- Rated static hook load, as stated on the manufacturer's nameplate
- Rig floor height, and clear height under the rotary beams
- Setback and rotary capacities, as stated by the manufacturer
- Whether the rig skids or walks between wells, and in which directions
- Number of truck loads and transport dimensions for a rig move
Documents to request from the seller
- Manufacturer, model and serial number, with photos of the nameplates
- Design drawings or the manufacturer's data book, if the seller holds them
- The most recent third-party inspection report, with its date and the name of the company that wrote it
- Records of any structural repairs or modifications, and who carried them out
- The rig-up and rig-down procedure the current owner uses
Masts and substructures listed on Oil Rigs Now: rig masts and rig substructures.
2 · Hoisting system
Crown block
What it does
The crown block is a set of sheaves (grooved pulleys) fixed at the top of the mast. The drilling line runs over these sheaves and down to the traveling block several times over. Each extra pass of line shares the load, which is how the drawworks can lift a long, heavy string of pipe with a single line.
Specs buyers compare
- Number of sheaves and sheave diameter
- Drilling line size the sheaves are grooved for
- Rated capacity, as stated on the nameplate
- The mast make and model it was built for, or a documented pairing with the mast on offer
Documents to request from the seller
- Nameplate photo showing manufacturer, model, serial number and rated capacity
- The most recent inspection report and its date
- Records of any sheaves that have been replaced
- Confirmation of which mast it came off, if it is offered separately
Crown blocks are normally sold with the mast or as part of a complete rig: see land drilling rigs.
3 · Hoisting system
Traveling block and hook
What it does
The traveling block is the moving set of sheaves that hangs from the drilling line inside the mast. It rises and falls as the drawworks reels line in and out. On a rig with a top drive, the top drive hangs below it. On older rigs a hook below the block carries the swivel and kelly. Some rigs use a block and hook combined in one unit.
Specs buyers compare
- Number of sheaves and sheave diameter, matched to the crown block
- Rated capacity, as stated on the nameplate
- Combined block-hook or a separate hook, and the hook's own nameplate rating
- How it connects to the top drive or swivel
- Overall length and weight, which affect usable travel in the mast
Documents to request from the seller
- Nameplate photos for the block and the hook, with serial numbers
- The latest inspection report and its date
- Records of sheave, bearing or hook repairs
- A written list of what comes as a set: block, hook, links and elevators
Traveling blocks are usually sold with the rig or the mast: see land drilling rigs.
4 · Hoisting system
Drawworks
What it does
The drawworks is the large hoist on the rig floor. Its drum winds the drilling line in and out to raise and lower the traveling block. A brake system holds and lowers the load. On modern AC rigs the drive motors do much of the braking as well, with an auxiliary brake behind them.
The drawworks input horsepower is usually the number a rig is named by: a 1,500 HP rig normally means a 1,500 HP drawworks.
Specs buyers compare
- Input horsepower and drive type (mechanical, DC or AC)
- Drum size and the drilling line diameter it is built for
- Gear and motor arrangement, or number of speeds
- Main brake type (band or disc) and auxiliary brake type
- Automatic driller or control system make and version
- Size and make of the drilling line on the drum, if line is included
Documents to request from the seller
- Nameplate photo, serial number and the manufacturer's model sheet
- Maintenance records, including brake and clutch work
- Motor and drive records for AC or DC units
- The drilling line's ton-mile log and the date the line was last replaced, if line is included
- Control system software version, and any licence or support agreement tied to it
See drawworks listed on Oil Rigs Now.
Rotating system
The rotating system turns the drill string so the bit can cut rock. On most modern land rigs that work is done by a top drive hanging in the mast. Older and smaller rigs turn the pipe from the rig floor with a rotary table and kelly. Many rigs carry both and keep the rotary table for handling pipe.
5 · Rotating system
Top drive
What it does
A top drive is a motor unit that hangs below the traveling block and turns the drill string from the top. It runs up and down guide rails in the mast. Because it can rotate the pipe and pump fluid through it while pipe is moving, it lets the crew drill with full stands rather than single joints. A pipe handler on the unit grips the pipe and helps make up and break out connections.
Specs buyers compare
- Make, model and year of manufacture
- Drive type (AC electric or hydraulic) and motor horsepower
- Continuous drilling torque and maximum make-up and break-out torque, as stated by the manufacturer
- Rated load capacity and maximum speed, as stated by the manufacturer
- Guide rail or torque track type, and whether it fits the mast it will go into
- Pipe handler, links and elevators included
- The drive house and control system it was last run with
Documents to request from the seller
- Serial number and the manufacturer's data sheet
- Service history, including any factory or authorized-shop overhaul and its date
- Operating hours since the last overhaul, if recorded
- A list of spares and tooling included
- The control system version, and a note of what it was last connected to
See top drives listed on Oil Rigs Now.
6 · Rotating system
Rotary table and kelly
What it does
The rotary table is the turning platform set into the rig floor directly over the well. Driven by its own motor or by the drawworks, it turns the kelly, a square or six-sided length of pipe that slides through a bushing in the table and passes rotation down to the drill string.
On a rig with a top drive, the rotary table still holds the pipe in slips while connections are made and broken.
Specs buyers compare
- Opening diameter, which sets the largest bit or casing that passes through
- Static load rating, as stated on the nameplate
- Drive type: independent motor or chain from the drawworks
- Maximum speed and torque, as stated by the manufacturer
- Master bushing, kelly bushing and slips included
- For kelly rigs: kelly size and shape, and the swivel make and model
Documents to request from the seller
- Nameplate photo and serial number
- Maintenance and overhaul records
- A list of bushings, inserts and handling tools included
See rotary tables listed on Oil Rigs Now.
Circulating system
The circulating system pumps drilling fluid, usually called mud, down the inside of the drill string, out through the bit and back up the hole. The mud carries rock cuttings to the surface, cools the bit and helps balance pressure in the well. At surface the cuttings are screened out and the cleaned mud returns to the tanks to be pumped again.
Circulating equipment tends to be bought and sold in packages (pumps with their motors, tanks with their solids control), so ask early exactly which pieces a listing includes.
7 · Circulating system
Mud pumps
What it does
Mud pumps are the large piston pumps that push drilling fluid down the hole. Most land rigs run two or three triplex pumps (three pistons each), driven by electric motors or diesel engines. Pump capacity limits how fast mud can be circulated, which matters more as wells get deeper and laterals get longer.
Specs buyers compare
- Make, model and input horsepower
- Number of pumps and how each is driven (AC motor, DC motor or engine)
- Stroke length and the liner sizes supplied
- Maximum discharge pressure and flow rate for each liner size, as stated by the manufacturer
- Fluid end type and material
- Charging pumps, pulsation dampeners and skid layout included
Documents to request from the seller
- Serial numbers for each power end and fluid end
- Overhaul history, including the date of the last power end rebuild
- An inventory of spare liners, pistons, valves and seats included
- Motor or engine records for the pump drives
See mud pumps listed on Oil Rigs Now.
8 · Circulating system
Standpipe and rotary hose
What it does
The standpipe is a steel pipe that carries mud from the pumps up one leg of the mast. At the top it connects to the rotary hose (sometimes called the kelly hose), a heavy flexible hose that runs to the top drive or swivel and moves with it. Between the pumps and the standpipe sits the standpipe manifold, a set of valves that routes the flow.
Specs buyers compare
- Working pressure rating of the standpipe, manifold and hose, as stated by the manufacturer
- Inside diameter and length of the rotary hose
- End connection types
- Number of standpipes and the valve layout of the manifold
Documents to request from the seller
- The manufacturer's certificate for the rotary hose, with its serial number and date of manufacture
- The most recent pressure test record for the hose and manifold, with its date and who performed it
- A manifold drawing showing valve sizes and ratings
See rotary hoses listed on Oil Rigs Now.
9 · Circulating system
Mud tanks and solids control
What it does
Mud tanks hold the active drilling fluid along with mixing and reserve volumes. Solids control equipment sits on top of them. Shale shakers screen out the cuttings first; desanders, desilters and, on many rigs, centrifuges then remove finer particles. Mixing hoppers and agitators keep the mud blended.
Specs buyers compare
- Number of tanks, total volume and how it splits between active, reserve and pill tanks
- Shale shaker make, model and count
- Degasser, desander, desilter and centrifuge makes and models
- Agitators, mixing pumps and hoppers included
- Tank dimensions and the number of loads to move them
- Whether the system is set up for water-based mud, oil-based mud or both
Documents to request from the seller
- An equipment list for each tank, with makes and serial numbers
- Tank drawings showing compartments and volumes
- Maintenance records for shakers, pumps and centrifuges
- An inventory of spare screens and parts included
See mud tanks and shale shakers listed on Oil Rigs Now.
Power system
The power system supplies energy to everything else. On most land rigs it starts with diesel or natural gas engines driving generators. The electrical output passes through a control house that delivers it to the drawworks, mud pumps, top drive and rotary table. Older mechanical rigs drive the same equipment straight from the engines through chains and a compound.
Because the power system ties every other system together, a mismatch here (a DC rig paired with an AC top drive, for example) can mean a rig package needs extra equipment before it can work.
10 · Power system
Engines and generators
What it does
Rig engines are large diesel or gas engines, each usually paired with a generator on a shared skid. A typical electric land rig runs three or four sets and brings them on line as demand rises. Some rigs can burn natural gas or a gas and diesel blend, and some can draw grid power where a connection is available.
Specs buyers compare
- Engine make, model and rated horsepower
- Generator make, rated output (kW) and voltage
- Number of sets
- Fuel type: diesel, natural gas or dual-fuel
- Emissions tier or certification the engines carry
- Recorded hours on each engine
Documents to request from the seller
- Serial numbers for each engine and generator
- Hour-meter photos for each engine
- Engine maintenance and overhaul records, including the date and hours at the last major overhaul
- Emissions certification paperwork, where it applies to the buyer's location
- Oil analysis records, if the owner kept them
See rig generator packages and diesel generator sets listed on Oil Rigs Now.
11 · Power system
Power control house (SCR or VFD)
What it does
The power control house is the enclosed building that takes generator output and delivers controlled power to each motor on the rig. On a DC rig it is an SCR house, which converts the generators' AC output into variable DC. On an AC rig it is a VFD house, which uses variable frequency drives to control AC motors.
The driller's controls connect to this house, so it also shapes how far the rig's equipment can be automated.
Specs buyers compare
- Type: SCR (DC) or VFD (AC)
- Make, model and year
- Number of generator and motor bays, and which motor each bay drives
- Total power rating, as stated by the manufacturer
- Control system and PLC make, and software version
- Enclosure and air conditioning type
Documents to request from the seller
- Electrical drawings, including the single-line diagram
- An equipment list with serial numbers for drives and switchgear
- Service records and any component replacements
- Software versions, licences and access passwords for the control system, and whether they transfer with the sale
Control houses are usually sold with the rig or a power package: see land drilling rigs.
Well-control equipment
Every drilling rig carries well-control equipment at the wellhead. The two main items are named below, with the paperwork buyers ask for.
12 · Well-control equipment
Blowout preventer (BOP) stack
What it does
The BOP stack is a set of large valves mounted on the wellhead below the rig floor. It works with the choke manifold, which routes flow from the well.
Documents to request from the seller
- Manufacturer, model and serial number for each component in the stack
- The manufacturer's data book
- Current certification paperwork, the date it was issued and the company that issued it
- The test records the seller holds
- A list of components that have been replaced, and where the replacements came from
See BOP stacks listed on Oil Rigs Now.
13 · Well-control equipment
Accumulator (BOP closing unit)
What it does
The accumulator, or closing unit, is the hydraulic unit that operates the BOP stack. It sits away from the wellhead, with control panels on the rig floor and at the unit itself.
Documents to request from the seller
- Manufacturer, model and serial number
- Certification paperwork and its date
- Drawings, and a list of the remote control panels included
- Service records the seller holds
See BOP control units listed on Oil Rigs Now.
The drill string
The drill string itself (drill pipe, heavyweight pipe and drill collars) is usually bought separately from the rig. Buyers compare size, grade, connection type and the inspection class shown on the seller's report, and ask for that report with its date. See drill pipe listed on Oil Rigs Now.
Documents for the whole rig package
Component paperwork is most useful when it adds up to a clear picture of the whole package. Before making an offer, buyers commonly ask for:
- A full equipment list (the rig inventory) with makes, models and serial numbers, matched to the photos
- Proof that the seller owns the rig or has written authority to sell it, and confirmation of any liens
- Where the rig is now, when it last worked, and how it has been stored since
- Dated photos and video of each major component
- The most recent whole-rig audit or inspection report, with its date and author
- A transport list: the number of loads, with dimensions and weights, for a rig move
- Export or import paperwork that applies, for a cross-border sale
Questions to ask a seller
- Why is the rig or component being sold? A fleet change or a move to a different rig class is a different story from a vague answer.
- When and where did it last work, and on what kind of wells? The answer tells you what the equipment was set up for.
- Has anything been removed since it last worked? Rigs in storage sometimes supply parts to other rigs. Ask for a list.
- Which items are in the price, and which are optional or extra? Get the answer in writing against the equipment list.
- Will the seller allow an independent inspection before closing? Ask who would carry it out and how access to the yard works.
- Which of the documents in this guide exist, and which do not? Missing paperwork is easier to discuss before an offer than after one.
- Are spares, tooling and manuals included? These are often stored apart from the rig and left out of photos.
Looking for a complete land rig or a single component? Browse land drilling rigs and oilfield equipment, or describe what you need on the request form.
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