The BCG study had been under enough criticism and scrutiny that industry groups contracted with the UC Davis Policy Institute to assemble an expert independent review panel. The Western States Petroleum Association (WSPA, which originally funded the BCG report), the Rockefeller Brothers Fund and the Alliance of Automobile Manufacturers requested the BCG report evaluation. Instead of supporting Big Oil, the reviewers found the study flawed on a number of fronts. For example, the BCG report missed "positive effects on the health and welfare of the citizens of California that could result from the implementation of AB32." The review panel also said the BCG study understated the benefits of AB32 on the economy; overstated the cost of industry compliance; and overstated harmful impact on California's oil refining industry. You can read a more detailed break-down on the situation over at the Natural Resources Defense Council.
Oil companies have been particularly irate that the Low Carbon Fuel Standard requires them to reduce carbon pollution from gasoline and diesel 10 percent by 2020.
The California Air Resources Board created the Low Carbon Fuel Standard (LCFS) to comply with AB32. CARB wants to reduce the amount of carbon in transportation fuels as a way to reduce the resulting greenhouse gas emissions. The BCG study and the resulting fallout isn't the first time oil companies have attempted to block LCFS and AB32. They also attempted to pass the Proposition 23 ballot initiative, which failed win voter approval in November 2010.