Looking on the internet deeply has found these results:

may have been is the most popular phrase on the web.

must have been 15,140,000 results on the web	may have been 112,100,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
"It Must Have Been Love" is a song written by Per Gessle and performed by the Swedish pop duo Roxette. The ballad became the duo's third #1 hit in the United �... "The experts from the London Zoo thought that this puma must have been in the possession of a private collector and somehow managed to�... Feb 11, 2014 ... Must have been can have two meanings� it depends on the text. Must have p.p. doesn't always mean that, for instance, something did not�... Mar 4, 2009 ... ... is not available right now. Please try again later. Published on Mar 4, 2009. Music video by Roxette performing It Must Have Been Love.	11 hours ago ... Ormoc ferry may have been overloaded; death toll rises to 61 ... in Batangas � Ormoc ferry may have been overloaded; death toll rises to 61. 3 days ago ... Harper Lee's 'Go Set a Watchman' May Have Been Found Earlier Than Thought. By SERGE F. KOVALESKI and ALEXANDRA ALTER JULY 2,�... The file ( filename .xls) may have been changed by another user since you last saved it. In that case, what do you want to do? Save a copy; Overwrite changes. May have been and might have been mean the same thing in American English, and are nearly always interchangeable. These two sentences are equivalent,�...

must have been

15,140,000 results on the web

may have been

112,100,000 results on the web

More popular!

"It Must Have Been Love" is a song written by Per Gessle and performed by the Swedish pop duo Roxette. The ballad became the duo's third #1 hit in the United �...
"The experts from the London Zoo thought that this puma must have been in the possession of a private collector and somehow managed to�...
Feb 11, 2014 ... Must have been can have two meanings� it depends on the text. Must have p.p. doesn't always mean that, for instance, something did not�...
Mar 4, 2009 ... ... is not available right now. Please try again later. Published on Mar 4, 2009. Music video by Roxette performing It Must Have Been Love.

11 hours ago ... Ormoc ferry may have been overloaded; death toll rises to 61 ... in Batangas � Ormoc ferry may have been overloaded; death toll rises to 61.
3 days ago ... Harper Lee's 'Go Set a Watchman' May Have Been Found Earlier Than Thought. By SERGE F. KOVALESKI and ALEXANDRA ALTER JULY 2,�...
The file ( filename .xls) may have been changed by another user since you last saved it. In that case, what do you want to do? Save a copy; Overwrite changes.
May have been and might have been mean the same thing in American English, and are nearly always interchangeable. These two sentences are equivalent,�...