Onshore oil and gas refers to drilling and production that happens on land. Offshore refers to operations conducted in ocean waters, from shallow coastal areas to deep sea environments thousands of meters from shore. The two share the same goal (extracting hydrocarbons from underground rock formations) but differ significantly in cost, complexity, risk, and the infrastructure required to get the job done.
How Onshore Operations Work
Onshore drilling takes place on land in a wide range of settings: deserts, plains, forests, farmland, and sometimes near populated areas. The equipment is relatively straightforward compared to offshore. A typical land-based drill site includes a derrick (the tall steel tower), a rotary system that turns the drill bit, mud pumps that circulate fluid to cool the bit and carry rock cuttings to the surface, and a blowout prevention system that keeps the well under control if pressure surges unexpectedly.
Setting up an onshore site is faster and cheaper than building a platform at sea. Crews can drive equipment to the location on trucks, connect to existing road networks, and pipe extracted oil or gas to processing facilities through land-based pipelines. When a well stops producing, the operator plugs it with cement, removes the surface equipment, and restores the land. The logistics are simpler at every stage, which is why onshore drilling has historically been the backbone of global oil production.
That simplicity extends to the workforce. Onshore crews typically work 12-hour shifts over periods of one to two weeks, then rotate off for leave. But unlike their offshore counterparts, they can go home at the end of a shift if the site is close enough to a town, and emergency services can reach them by road.
How Offshore Operations Work
Offshore drilling happens on the ocean, anywhere from a few miles off the coast to hundreds of miles out in open water. Because you can’t just set up a rig on the sea surface, offshore operations require massive, purpose-built structures. The type of structure depends on how deep the water is.
- Jack-up rigs work in shallow water, roughly 25 to 150 meters deep. They have legs that extend down to the seafloor, lifting the platform above the waves. These are the most common type for near-shore drilling.
- Semi-submersible rigs float on large pontoons and are anchored in place, operating in water depths of 500 to 3,000 meters. Their partially submerged design makes them more stable in rough seas.
- Drillships are exactly what they sound like: ships equipped with drilling equipment. They can operate in the deepest water, up to about 3,650 meters, and use GPS-guided thrusters to hold position over the wellhead.
All of these platforms need to be self-sufficient. They generate their own power, house their own crews, process drilling fluids, and manage well control systems, all while dealing with waves, wind, and corrosive saltwater. Supplies arrive by helicopter and supply vessel. Once oil or gas is extracted, it travels to shore through subsea pipelines or is loaded onto tanker ships.
Depth Classifications
The offshore world is further divided by water depth. The current industry consensus, established at the 2002 World Petroleum Congress, defines water shallower than 400 meters as normal depth. Water between 400 and 1,500 meters is classified as deepwater, and anything beyond 1,500 meters is ultra-deepwater. These classifications matter because cost, technical difficulty, and risk all escalate sharply as water gets deeper. A deepwater well can cost several times more than a shallow-water well, and ultra-deepwater projects are among the most expensive engineering undertakings in any industry.
Cost Differences
Onshore drilling is significantly cheaper. A land-based well can often be drilled with standard equipment that’s trucked to the site, and operational costs stay relatively low because everything is accessible by road. Offshore drilling, by contrast, requires building or leasing a platform, transporting crews and supplies by sea and air, and maintaining equipment in a corrosive marine environment. The deeper the water, the higher the bill. Ultra-deepwater projects can run into billions of dollars before the first barrel of oil reaches a refinery.
This cost gap is why onshore drilling dominates global production. Offshore projects only make economic sense when the reserves are large enough to justify the investment, or when onshore reserves in a region have already been tapped.
Environmental Risks
Both settings carry environmental risks, but the nature of those risks differs. Onshore drilling can contaminate groundwater, especially when hydraulic fracturing is involved. Fracturing requires large volumes of water mixed with chemicals to crack underground rock, and faulty well construction or improper handling can allow those fluids to leak. The process also generates large amounts of wastewater that may contain dissolved chemicals, which is typically disposed of by injection into deep saltwater wells. Clearing vegetation for drill sites disrupts local ecosystems, and significant water use for oil production can affect availability for other purposes in some regions.
Offshore drilling poses different threats. Oil spills in ocean water can devastate marine ecosystems and coastal communities over vast areas. Seismic surveys used to map underground formations may harm fish and marine mammals. And when something goes wrong on an offshore platform, the remote location makes containment and cleanup far more difficult than on land.
Workforce and Daily Life
Working offshore is a fundamentally different experience from working onshore. On a typical North Sea installation, personnel work two-week tours with 12-hour shifts, day and night, then fly home for two to four weeks of shore leave depending on the country. Norwegian workers generally follow a two-weeks-on, four-weeks-off schedule, while UK workers more commonly rotate two-on, two-off or two-on, three-off.
During those two weeks offshore, workers live in confined quarters on the platform itself. They’re isolated from family, exposed to unpredictable sea and wind conditions, and performing safety-critical tasks around hazardous industrial processes. This combination of long shifts, confined living space, and physical isolation creates workforce challenges that don’t exist onshore, where crews can leave the site between shifts and emergency responders are a short drive away.
What Happens When a Well Runs Dry
Every oil or gas well eventually stops producing enough to be worth operating. At that point, decommissioning begins. For onshore wells, this means plugging the well with cement, removing surface equipment, and restoring the land.
Offshore decommissioning is far more complex and expensive. The well must be permanently sealed to protect the marine environment. Then the platform’s superstructure is dismantled and either sold as scrap metal or refurbished for use elsewhere. The substructure, the part that sits below the waterline, is typically cut off about 15 feet below the seafloor and hauled to shore. In the U.S., federal regulations require companies to remove platforms within one year after a lease expires, preventing abandoned structures from accumulating in the ocean. In some cases, regulators allow a retired platform to be converted into an artificial reef rather than fully removed, provided it meets federal requirements.
The Bureau of Safety and Environmental Enforcement enforces an “Idle Iron” policy specifically to prevent non-producing wells and inactive structures from lingering in the Gulf of Mexico. Companies must dismantle infrastructure and responsibly dispose of it after plugging wells that are no longer in use.