What happened

Shares of United Parcel Service (NYSE:UPS) stock jumped in post-Christmas trading and are up 6.3% as of 3:35 p.m. EST. No one factor appears to be behind the sudden strength in UPS shares. Rather, three factors appear to be behind it.

First, on Wednesday, Mastercard's SpendingPulse market-research service reported that online spending was up 19.1% year over year in the period running from November 1 through December 24 -- which suggests that companies like UPS, which ship such online orders, should benefit similarly. Second, CNBC is, in fact, confirming today that "shipping companies [saw] record e-commerce deliveries" in the Christmas delivery season.

Stacks of delivery boxes.

Christmas is a busy time for parcel shipment -- and parcel shipment stocks like UPS. Image source: Getty Images.

So what

Third, this morning, analysts at Standpoint Research initiated coverage of UPS stock with a buy rating. Granted, so far there's little detail available on Standpoint's rationale for rating UPS a buy. Regardless, three positive news items in a row seem like it should be enough to lift a stock, and true to form, investors are bidding up UPS big-time.

Now what

Will UPS be able to hold onto today's gains? That depends.

For one thing, while overall "online spending" was up 19.1%, that doesn't necessarily mean that the increase in spending went to retailers that use UPS to deliver their packages. Amazon, in particular, has been working hard lately to handle more of its package delivery on its own, including through the use of services such as Amazon Air. It remains to be seen how big a proportion of this year's holiday sales gains will benefit UPS -- and by how much.

For the time being, however, the outlook appears positive.