The SSRA does the best it can to ensure fair racing and a level playing field for all competitors. To this end, they have acquired fuel testing equipment have have made extensive use of it with hundreds of samples being tested.
ISR rules do not allow the use of power adding substances in fuel. These include but are not limited to nitrates and oxygenators. Higher octane is not a concern and it is not octane that is measured. Higher octane fuel actually burns slower, lending to it's most usefull property, detonation resistance. What the rules are concerned with are power adding substances in the fuel. There are very simple and efficient methods of testing for these and the results are very consistent.
But what does that mean for the racer? Race fuels are ok as long as they do not contain any of the power adding substances. If the fuel you plan on using claims a boost in horsepower in its advertising, it probably will not pass the fuel tests. Some examples of fuels in the VP lineup which are ok to use are the popular C12 and C14 blends. Popular examples of fuels which will not pass are any of the "U" or "MR" fuels and DRT (to name just a few). These fuels are heavy in oxygenators.
As a rule, gasoline purchased at the pumps is OK as long as the competitor does not add anything to it. The SSRA has found many circumstances where the fuel failed even though the racer claimed it was purchased at the pump. Indeed the fuel was purchased at the pump but additives were then mixed in. Some of the additives that were used and caused fuel to fail included OE brand fuel conditioners and de-icers, octane boosters (not because of the octane boost but because of the other additives in the product), NOS brand additives and several other types of additives containing nitromethane.
In field testing of fuel, it is simply a "pass" or "fail" situation. The sactioning body does not have to provide an indepth chemical analysis to determine exactly what brand addtives are there. Rather, they just determine whether they are there or not. The equipment used is very consistent, quick and accurate.
Fuel testing, while sometimes a source for some heated discussion, has been found to tighten the competition significantly and contribue to fair racing.