Oil prices increased faster than gas prices on the way up. If gas had increased as much as oil then the price at the pump would have been US $6.00.
If you remember the refineries were reporting lower profits because of this.
Here is a quote
from an article back in June.
"Companies that refine oil to produce gasoline and other products have been struggling to pass soaring crude price on to their customers. While oil in the U.S. has nearly doubled in the second quarter, gasoline prices are up only 25.0%."
Here is the data.
Source:
http://tonto.eia.doe.gov/dnav/pet/pet_pri_top.asp
Gas crude
Jun 310 67.49
Jul 301.3 74.12
Aug 283.3 72.36
Sep 283.9 79.91
Oct 284.3 85.8
Nov 311.8 94.77
Dec 306.9 91.69
Jan 309.6 92.97
Feb 308.3 95.39
Mar 330.7 105.45
Apr 349.1 112.58
May 381.3 125.4
Jun 411.5 133.88
Jul 414.2 133.37
You can see here that oil almost doubled from June til August while gasoline only increased by about 34% for the same period.