For interest and as a reference, you might like to read/revisit the CAA's report on UK air operators' fuel planning policies. This report, which was based upon information obtained in the Summer of 2000, describes JAR-OPS 1 fuel policy and how various operators specified these requirements for the aeroplanes they operated. In particular, the report addresses reserve fuel.
The report can be accessed through
www.chirp.co.uk>>confidential reports>>library.