Left field question

[Hammer65]

Here's some data from a Roush 427SR in a Superformance MKIII

Date Miles Gallons Cost $/Gal MPG Average
5/10/2008 63 14.64 $60.57 $4.14
5/15/2008 154 8.12 $34.11 $4.20 11.2 11.2
5/17/2008 290 12.89 $54.38 $4.22 10.6 10.8
7/9/2008 652 14.69 $68.71 $4.68
7/13/2008 748 8.87 $41.51 $4.68 10.8 10.8
7/17/2008 879 14.03 $63.41 $4.52 9.3 9.9
7/20/2008 1002 11.15 $50.16 $4.50 11.0 10.3
8/4/2008 1128 11.97 $53.62 $4.48 10.5 10.3
8/7/2008 1259 11.88 $52.00 $4.38 11.0 10.5
8/18/2008 1351 8.56 $36.62 $4.28 10.8 10.5
8/29/2008 1481 12.44 $52.46 $4.22 10.5 10.5
9/7/2008 1587 8.88 $36.21 $4.08 11.9 10.7
9/16/2008 1715 13.89 $57.49 $4.14 9.2 10.5
11/23/2008 1815 9.62 $24.51 $2.55 10.4 10.5
3/29/2009 1939 12.68 $33.47 $2.64 9.8 10.4
4/25/2009 2080 13.08 $34.79 $2.66 10.8 10.4
5/17/2009 2226 13.58 $38.83 $2.86 10.8 10.5
8/19/2009 2621 13.23 $42.58 $3.22 9.6
9/17/2009 2732 12.42 $41.96 $3.38 8.9 9.6
3/22/2010 2849 11.61 $39.01 $3.36 10.1 9.6
5/13/2010 2975 13.10 $45.31 $3.46 9.6 9.6
7/7/2010 3138 14.45 $50.86 $3.52 11.3 9.7
7/28/2010 3292 13.24 $45.01 $3.40 11.6 9.8
30/2010 3430 12.44 $43.04 $3.46 11.1 9.9
10/19/2010 3557 15.17 $52.15 $3.44 8.4 9.8
5/20/2011 3689 12.32 $52.95 $4.30 10.7 9.8