* Gasoline demand down 1.6 pct wk/wk, up 2.8 pct yr/yr
* Four-week average demand up 0.1 percent year-on-year
NEW YORK Feb 5 (Reuters) - U.S. retail gasoline demand rose by 2.8 percent last week compared with the same period a year ago, MasterCard said on Tuesday, in data that shows the first signs of stabilizing demand after a slide for most of 2012.
For the past four weeks, demand was 0.1 percent higher on average compared with the same period a year ago, Mastercard said in its SpendingPulse report, even as demand slipped by 1.6 percent against the previous week as prices rose.
"The four-week year-over-year metric began to turn to positive territory ... the first growth rate since the week ending Sept. 21, 2012, and only the second time in over a year," said John Gamel, gasoline analyst for the Mastercard Advisors SpendingPulse report.
The average price of gasoline across the United States was $3.41 a gallon last week, 8 cents higher than the previous week.
The largest price spikes were in the Midwest and the Rocky Mountain region, although the latter still enjoys some of the lowest average prices in the United States at $3.04 a gallon.
The Lower Atlantic region experienced the smallest rise in prices, up 5 cents to $3.39 a gallon.
Compared with a year ago, the average price of gasoline was down nationally by 1.7 percent and was lower across all regions apart from the Midwest, where prices were 0.6 percent higher, and New England, where prices were flat.
"Overall, we will have to observe if the year-over-year comparisons continue to remain positive and therefore indicate an upward trend in gasoline demand, especially if prices continue to rise," Gamel said.
MasterCard Advisors, a unit of MasterCard Inc, estimates retail gasoline demand based on aggregate sales in the MasterCard payments system, coupled with estimates for other payment forms including cash and checks.