Though Lady Gaga coming in at #1 on a list of top-earning female musicians isn't really much of a surprise, the monetary gap between Mother Monster and the #2 earner - country music sensation Taylor Swift - is incredibly stark, with the former taking in a whopping $90 million vs. Swift's paltry $45 million. 

So how did Gaga make so much money in the stretch spanning from May 2010 through May 2011 (the time period in which Forbes took into account each stars' pre-tax earnings?) For one thing, her concert sales are unrivaled in pop music, where the singer takes in - according to Forbes - a $1.3 million nightly gross while on tour. Add to that big album sales (her "Born This Way" was released on May 23, 2011) and several lucrative endorsement contracts with companies like Polaroid and Virgin Mobile, and you've got yourself one wealthy entertainer.

As for Swift - not exactly a slouch in the earnings department - the pop-country star brings in an estimated $1 million a night while on tour, while her last album, 2010's "Speak Now", sold over a million copies Stateside in its first week alone.

The other slots in the top ten are occupied by more or less the usual suspects, all of them working in the pop-music field - the genre of music which by its very nature holds the widest possible audience appeal. Here's how the rest of the list shakes down:

3) Katy Perry, $44 million

4) Beyonce, $35 million (which Forbes describes as a "dip in earnings", oh poor B)

5) Rihanna, $29 million

6) Pink, $22 million

7) Carrie Underwood, $20 million

8) Celine Dion, $19 million (thanks mostly to her Vegas show bringing in an estimated $2.3 million nightly!)

9) Adele, $18 million

10) Britney Spears, $10 million and Alicia Keys, $10 million (tie)

What do you think of the list? Anyone you're surprised to see here? Anyone you thought would've made the cut but didn't? Sound off in the comments section below!