The Tengiz Field in Kazakhstan is one of the world's 10 largest crude oil fields — and one of the most complex to produce. The crude oil is high in hydrogen sulfide gas, and the reservoirs must be maintained at ultra-high pressures in order to maximize production. Two expansion projects of extraordinary scope have overcome both challenges and almost doubled production capacity to 540,000 barrels of crude oil, 760 million cubic feet of natural gas and 46,000 barrels of natural gas liquids per day. One project called for building the largest facility in the world for processing crude oil and separating out the hydrogen sulfide gas. The second included a specially designed compressor that reinjects one-third of the gas back into the reservoir at the highest pressures ever achieved. The gas helps maintain reservoir pressure and acts as a solvent, sweeping additional crude oil toward producing wells.