The U.S. has purchased two Su-27 fighters from Ukraine. They were delivered in a Ukrainian An-124 transport. The Su-27s will be used to help train American pilots to cope with the growing number of Su-27 and Su-30 fighters being sold to air forces the world over. The two Su-27s will also be used to test the effectiveness of new U.S. radars and electronic warfare equipment.
Russia's Sukhoi aircraft company has sold over a billion dollars worth of these aircraft (plus components and technical services for them) a year for the last few years. Sukhoi mainly supplies Su-27/30 jet fighters to India, China, Malaysia, Venezuela and Algeria. The 33 ton Su27 is similar to the U.S. F-15, but costs over a third less.
Developed near the end of the Cold War, the aircraft is one of the best fighters Russia has ever produced. The government helped keep Sukhoi alive during the 1990s, and even supplied money for development of an improved version of the Su-27, which was called the Su-30. This proved to be an outstanding aircraft, and is the main one Sukhoi produces. There are now several Su-30 variants, and major upgrades. While only about 700 Su-27s were produced (mostly between 1984, when it entered service, and the collapse of the Soviet Union in 1991), adding Su-30 production and you have over 1,000 aircraft (including license built ones in China and India).