Series-parallel hybrids have the flexibility to operate in either series or parallel mode. As a result, they are more efficient overall because they can operate as a series hybrid at lower speeds and as parallel at high speeds, but their cost is higher than a pure parallel.
Hybrid powertrains currently used by Ford, General Motors, Lexus, Nissan, and Toyota (Toyota Highlander pictured at left), which some refer to as “series-parallel,” can operate in both series and parallel mode at the same time.