Are the most common type of offshore drilling rig, and tend to be the most volatile in terms of rates and demand. Jackups have a barge section that floats on the water (and holds the drilling equipment) and multiple legs (typically three, but sometimes more) that extend down to the sea floor. Jackups are typically towed to the targeted drilling site and, upon arrival, the legs are jacked down to the sea floor.
Once in place, these platforms are typically steady and sturdy, with a drilling platform well above the waves. Because they do physically touch the bottom of the sea floor, they are generally only usable in relatively shallow water – up to around 400 feet of water. Most jackups drill down through holes in the platform, but some (called "cantilevered") drill over the side of the barge.
Are quite a bit different than jackups. Semisubmersibles float on submerged pontoons and have an operating deck that is well above the surface. Below the surface are anchors and umbilicals that essentially tie the rig in place, though some do have powered systems that can help keep the rig on target.
With succeeding generations, the capacity of these rigs has increased, and the most modern generation of semi-submersibles can operate in up to 10,000 feet of water. While jackups can earn high day rates in specific circumstances, semisubmersible rates tend to be three- to five-times higher.
Like semi-submersibles, drillships can operate in a wide variety of circumstances, and are often used in locations with very deep water. Like semi-submersibles, drillships typically have an operating limit of 10,000 feet – a limitation that has more to do with extending a drilling operation through that much water as opposed to any limitations of the ship itself.
Drillships basically look (and operate) like very large boats, with drilling taking place through a hole in the hull (called a moon pool). These ships are completely independent and self-powered. While not as stable as semisubmersibles, drillships are mobile and can carry a lot of equipment – making them a good option for drilling exploratory wells. Like semisubmersibles, day rates for drilling ships are often quite a bit higher than those for jackups.