US online sales jumped 15 percent this holiday season, spurred by “aggressive” marketing by Web-based retailers, a research firm said.

Online sales were $36.4 billion from Oct. 31 through Dec. 22, compared with $31.5 billion a year earlier, said MasterCard Advisors’ SpendingPulse.

Online apparel sales grew fastest, rising 26 percent, with electronics up 12 percent.