Online spending in April increased 19.2% year over year, the sixth straight month of double-digit growth for e-commerce, according to an estimate released today by MasterCard Advisors, the consulting arm of MasterCard Worldwide. E-commerce spending increased 16.1% year over year in March.

MasterCard bases the SpendingPulse report on retail sales using all payment forms, including credit and debit cards of all brands, cash and checks. As is often the case, this month’s report did not include actual spending in dollars.

Online sales of shoes increased 20% year over year in April, with online sales of women’s apparel increasing about 15%, the second straight month that the women’s apparel e-commerce category has grown by at least 15%, MasterCard says. Total apparel sales, which also include bricks-and-mortar stores, increased 10.4% in April, helped by Easter sales, the report says.

Online sales of consumer electronics grew 9.1%, the eighth straight month of growth for that category. By contrast, overall sales of electronics and appliances, including products sold in bricks-and-mortar stores, declined 1.8% year over year in April.

MasterCard says rising gas prices likely will boost online sales. “We can expect consumers to make fewer shopping trips, especially on weekends, and this may contribute to an ever stronger growth for e-commerce,” says Michael McNamara, vice president, research and analysis for MasterCard Advisors SpendingPulse.

This month’s report offered no more e-commerce figures, but did note that overall luxury sales had its seventh consecutive month of growth, up 9.6% year over year, the largest monthly gain since May 2010.