EL PASO—Gas prices have been on a roller coaster ride since the beginning of the year, but the days of filling up a car with a crisp $20 bill may be a possibility for the summer. Gas prices started to rise again at of the end of January, reaching $2.42 in February and have since slowly decreased as the maintenance of refineries in the U.S. have finished and have gone online worldwide. “Other cities are more geographically compact because they don’t have mountain ranges or military bases preventing them from getting to their destination. We tend to use a lot more gasoline per capita in El Paso,” said Tom Fullerton, professor of economics and finance at the University of Texas at El Paso. “So when gasoline prices go down, it helps us a lot.