Bruno Mars [1] holds atop the Billboard Hot 100 [2], as "Locked Out of Heaven" spends a fourth week at No. 1. Taylor Swift [3]'s "I Knew You Were Trouble.," meanwhile, continues its play for the top, pushing 4-2, and PSY [4]'s "Gangnam Style" re-enters the top 10.

As it maintains its command over the Hot 100, "Heaven" spends a second week at No. 1 on Radio Songs [18], logging a less than 1% increase to 140 million all-format audience impressions, according to Nielsen BDS. "Heaven" relinquishes its three-week rule on Digital Songs, falling 1-2 despite a 120% gain to 497,000 downloads sold, according to Nielsen SoundScan. As previously reported [LINK to Billboard 200 story], sales during the Dec. 24-30 tracking week soared as consumers cashed in on digital retailers' gift cards, a tradition of the decade-old digital era; all titles but three in the Digital Songs top 50 this week gain by at least 100%.

"Heaven" likewise slips 1-2 on On-Demand Songs after two weeks on top, decreasing by 5% to 1.03 million on-demand streams, according to BDS.

Swift's "Trouble" leaps 4-2 with the Hot 100's top Digital Gainer award for a third week. The song reaches a new peak, having bounded onto the Hot 100 at No. 3 nine weeks ago as a then-preview cut to her album "Red," arriving that week (Oct. 27) at No. 1 on Digital Songs (416,000). The second pop radio single from the set returns to the Digital Songs apex with a 164% gain to 582,000 downloads sold, marking the fourth-best weekly sales sum of the digital era, two of which belong to Swift: "Trouble" trails only Flo Rida [19]'s "Right Round" (636,000, Feb. 28, 2009), Swift's "We Are Never Ever Getting Back Together" (623,000, Sept. 1, 2012) and Ke$ha's "TiK ToK" (610,000, Jan. 9, 2010). With its latest frame, "Trouble" passes 2 million downloads sold to date.

BILLBOARD 200: Taylor Swift's 'Red,'
'Les Mis' Soundtrack Lead [20]

"Trouble" retreats 11-12 on Radio Songs, although with a 5% uptick to 67 million. (It's not available to subscription streaming services and, thus, does not appear on On-Demand Songs.)

Despite Swift's swell in sales momentum, "Heaven" boasts a lead of more than 10,000 overall Hot 100 chart points over "Trouble." The latter title, however, gains by more than twice as much (up 113%) as the former (up 49%), pushing Swift closer to her potential second No. 1, following "Together" (which reaches 3 million in total digital sales).

Rihanna [21]'s former three-week Hot 100 No. 1 "Diamonds," atop R&B/Hip-Hop Songs for a 13th week, descends 2-3. It returns (2-1) for a sixth week atop On-Demand Songs with 1.07 million on-demand streams (up 2%) and 1.29 million streams overall; holds at No. 2 on Radio Songs (132 million, down 2%), which it led for three weeks; and is a non-mover at No. 5 on Digital Songs, although up 159% to 365,000) after ruling the ranking the week of Dec. 1. It, too, crosses the 2-million sold-to-date barrier.

The Lumineers [22]' "Ho Hey" regresses 3-4 on the Hot 100, while leading the Rock Songs chart for a fifth consecutive week, and Justin Biebe [23]r's "Beauty and a Beat," featuring Nicki Minaj, holds at No. 5 on the Hot 100. With 372,000 downloads sold last week (up 212%), "Beauty" passes 1 million in sales to date (1.29 million).

Powered by consumers purchasing some of 2012's most buzzworthy hits and radio airplay recounting the same in year-end retrospectives, PSY's "Gangnam Style" gallops back into the Hot 100's top 10 (19-6). The song peaked at No. 2 for seven weeks in October and November and had last ranked in the top 10 the week of Dec. 15. "Style" soars 8-3 on Digital Songs with a 245% gain to 400,000 downloads sold, marking its best weekly total. (It's sold 3.6 million since its release.)

Rounding out the Hot 100's top 10, Ke$ha [24]'s No. 2-peaking "Die Young" drops 6-7 (and is the top bracket's third title to pass 2 million downloads sold), followed by Maroon 5 [25]'s "One More Night" (7-8); Phillip Phillips [26]' "Home" (9-9); and Macklemore and Ryan Lewis [27]' "Thrift Shop" (10-10), which sold 304,000 downloads last week (up 116%), pushing it past 1 million in to-date sales.

Among highlights below the Hot 100's top 10, rapper A$AP Rocky's "F**kin Problems," featuring Drake, 2 Chainz and Kendrick Lamar, claims top Streaming Gainer honors, despite descending 24-26. The track vaults 24-13 on On-Demand Songs (553,000, up 11%).

In addition to PSY benefiting from nostalgia-fueled year-end airplay and sales surges, the top two songs of 2012 rebound on the Hot 100. Gotye [28]'s "Somebody That I Used to Know," featuring Kimbra [29], last year's top Hot 100 title, rises 49-48 (in its 52nd week) with top Airplay Gainer kudos, roaring 45-24 on Radio Songs (up 63% to 41 million). (Adult contemporary radio returning to regular programming after Christmas Day also aids the song's advance, as "Somebody" re-enters the Adult Contemporary chart at No. 1, marking its 17th nonconsecutive frame on top.) 2012's runner-up song, Carly Rae Jepsen [30]'s "Call Me Maybe," charges 43-27 on the Hot 100, up 65-36 on Radio Songs (33 million, up 61%).

Check Billboard.com [2] later today (Jan. 3), when all rankings, including the Hot 100 and On-Demand Songs in their entirety and Digital Songs and Radio Songs, will be refreshed, as they are each Thursday; due to the New Year's holiday, all charts are updating later than usual today (around 6 p.m.)