Milwaukee’s average gas price hit $3.05 per gallon this week, a three-year low, which was lower than Wednesday’s national average gas price of $3.22 per gallon.

Milwaukee experienced the trend of falling prices by about $0.20 this past week, while the national average decreased by $0.16, according to milwaukeegasprices.com. At this time last year, Milwaukee saw an average gas price of $3.37 and hit an all-time high in March 2012 at $4.21 per gallon.

“Changes in gas prices ultimately come down to supply and demand,” said Brian Brush, a professor of economics. “Changes in price can be seasonally based. More people drive in the summer so you can usually see an increase around Memorial Day and a decrease in the fall.”

Brush said many times price changes are a result of regulation that changes production standards.

“The EPA requires different blends at different times of the year, this may cause refineries to curtail production,” Brush said.

According to US World News & Report’s College Rankings, 20 percent of Marquette students have cars on campus. Many students leave the city to fill up on gas because prices south toward Kenosha and north toward Brown Deer are cheaper.

Paul Seifert, a junior in the College of Engineering, makes a three-hour total commute to work in a co-op in McHenry, Ill., during the week, while still living on campus.

“I fill up mostly in Illinois,” Seifert said. “More gas stations are conveniently located along my drive that aren’t as expensive as Milwaukee.”

Zipcar, the car sharing service, is a popular option for many college students because gas and insurance are included in the monthly subscription and hourly rates. Two zipcars are on campus that are available for students.

“Zipcar is really handy for errands,” said Jasmine Hempel, a junior in the College of Communication. “Since we don’t have a grocery within walking distance, it’s helpful.”

One of the factors in determining gas prices is the price of crude oil per barrel. According to a weekly AAA news release, the price of West Texas Intermediate crude oil was under $100 per barrel for three consecutive weeks.

“While AAA does expect the national average price at the pump to continue to fall approaching the end of the year, and many motorists will enjoy local prices below $3 per gallon, the national average is unlikely to breach this threshold,” the news release stated. “The last time the national average registered less than $3 was December 22, 2010.”

Brush said the many factors affecting gas prices are domestic, but global factors can influence the price of gas as well.

“For example, the growth of China and India has put an upward pressure on the price of crude oil,” Brush said. “Beyond that things like weather events can also disrupt transportation of inputs.”

The U.S. low gas price as of Wednesday was $2.89 in Oklahoma, and the high was $3.94 in Hawaii.