I dont have my 727 book handy, but become very familiar with the Company Fuel Policy pages at the front. The table on its side lists the reserves et cetera that you need for each situation, normal ops, normal+alternate, OEI, DP.
But dont forget that for in-flight planning, the reserves required are less than for pre-flight planning. Off the top of my head, I think the 45 min fixed reserve can be dropped to a 30 min fixed reserve, provided the aircraft has already taken off. The page before the fuel policy table explains this. Sorry I dont have page numbers.