Biogasoline, which contains 7 vol% of bio-ETBE (ethyl t -butyl ether), began circulating in the Metropolitan area of Japan on April 27, 2007. Among 44,000 gas stations in Japan, biogasoline is currently sold only in 100 gas stations. Name and location of these 100 gas stations are disclosed. If biogasoline is truly sold only in these gas stations, tracking a gasoline sample back to its retailer will be possible; when ETBE is detected in a gasoline sample, it is certain that the sample was sold in one of the 100 gas stations. Biogasoline was collected in the end of June, September, December 2007 and March 2008 from gas stations of 3 different brands in Chiba prefecture, and its color, density, composition and concentration of ETBE were analyzed. Regular gasoline was also collected from gas stations of the same 3 brands for comparison. GC/MS analysis revealed that biogasoline of 3 different brands was identical, suggesting that adulteration of biogasoline by mixing with regular gasoline was not carried out. ETBE was not detected from any sample of regular gasoline at all. Absence of ETBE in regular gasoline indicates that handling of biogasoline was strictly regulated, making the tracking of biogasoline sample back to its retailer possible.