Not sure when the engine was upgraded (2008 maybe?) but a 325i with the N53 direct injection engine produces way better economy figures than those quoted so far in this thread. I get lower 30s around town and 40+ on motorways...
http://www.e90post.com/forums/showthread.php?t=18241
__________________
E92 pre-LCI 325i - Ohlins R&T; H&R spacers; M3 strut brace; Swift thrust sheets; 3 x chassis braces; diff brace; N53 V-brace; 034 subframe inserts; BMS clutch stop; BMS CDV; RE g/box mounts; Delrin shift bushes; Saikoumichi OCC; Cyba scoops; BMW Perf Exhaust; HEL s/steel brake hoses; M3 rear spoiler; Recaro Sportster CSs; M3 white dash LEDs; LED Angels; LED side repeaters; BMW Perf black grille; CSL reps; SSDD carbon diffuser; Monster Wrap black roof/clear front