FLANKERS FOREVER: A COMPREHENSIVE LISTING OF SU-27 VARIANTS: 
Su-27: Basic long-range strategic air superiority fighter, built by KnAAPO., 
Su-27IB: Prototype of the Su-34, Su-27IBP: Prototype of the electronic warfare version of the Su-34, 
Su-27K: Carrier-based long-range strategic air superiority fighter, built by KnAAPO, 
Su-27KM: A prototype of a new carrier fighter, basically an Su-33 with the Su-35 weapons, 
Su-27KPP: Carrier-based electronic warfare aircraft, derivative of Su-33, 
Su-27KRTs: Carrier-based recon aircraft prototype, used for target designation, 
Su-27KU: An old project for a side-by-side trainer variant of a carrier-based fighter, 
Su-27KUB: Current project for a carrier-based side-by-side two-seat fighter, 
Su-27M: Prototype of Su-35 advanced multi-role fighter, 
Su-27P: Basic interceptor version for Air Defense forces.
Su-27PD: Prototype with in-flight refueling. Personal aircraft of Anatoly Kvochur.
Su-27PU: Prototype of tandem two-seat superiority fighter built by IAPO.
Su-27R: Recon version of Su-34. Active project but not yet in service.
Su-27SK: Export version of Su-27 built by KnAAPO.
Su-27SMK: Export multi-role version of Su-27, offered by KnAAPO.
Su-27UB: Tandem two-seat trainer version of Su-27, built by IAPO.
Su-27UBK: Export version of the Su-27UB.
Su-30: Tandem two-seat air superiority fighter built by IAPO.
Su-30K: Export version of Su-30.
Su-30K2: Side-by-side two-seat version, being built by KnAAPO.
Su-30KI: Proposed version of the Su-30 for sale to Indonesia, includes in-flight refueling for extended over-ocean operations.
Su-30MK: Generic designation for all multi-role two-seat tandem versions of the Su-27.
Su-30MKI: Version in production by IAPO for sale to India. Includes tandem triplane configuration and advanced fire control.
Su-30MKK: Version in production by KnAAPO for sale to China.
Su-30MKR: Version of the tandem-seat aircraft for use by the Russian Air Force. The airframe is that of the Indian version, but all electronics are Russian.
Su-32FN: Land-based maritime patrol export version of the Su-34.
Su-32MF: Multi-role export variant of the Su-34.
Su-33: Carrier-based air-superiority fighter.
Su-33UB: Carrier-based two-seat side-by-side fighter, not yet in production.
Su-34: Two-seat side-by-side deep strike aircraft.
Su-35: Advanced multi-role fighter.
Su-35K: Listed as attending the 1995 Paris Air Show but did not do so. Described as a maritime fighter.
Su-35UB: Same as Su-30MKK but made by KnAAPO instead of IAPO.
Su-37: Final derivative to date. Includes new avionics and thrust-vectoring engines. --Stephen V Cole