The operational performance of the JET Neutral Beam Injector (NBI) system during 2003 is presented and compared with NBI operation from 1994 to 2002. The paper also addresses different demands imposed on NBI operation during the JET Joint Undertaking (until the end of 1999) and the European Fusion Development Agreement (EFDA) JET Operating Contract (from 2000). The material presented shows new operational performance records achieved in 2003, derived from data focused on average and maximum pulse lengths, pulse power and injected pulse energy. Over the last ten years the issue of JET NBI PINI reliability and availability has also been of significant interest. A discussion is presented where terminology is defined, specific technical systems causing unreliability and non-availability are analysed and operational practices are reviewed. The performance analysis shows that during the period of JET operation under the EFDA contract, the NBI facility has successfully changed from high power - short pulse to high power - long pulse (10s) operation. It also shows that the sources of unreliability and non-availability have largely remained constant during this change.