Almost half of the money made by professional authors is earned by just 5% of writers, according to a study of authors' earnings in the UK.
The top 5% of authors earned 42% of all income received by professional writers in 2013, according to The Authors' Licensing and Collecting Society.
Meanwhile, the bottom half of professional writers accounted for just 7% of all authors' earnings overall.
The society said last year that writers earned 29% less in 2013 than 2005.
"The creative industries are thriving, generating £76bn per annum, yet professional writers have seen a near 30% reduction in earnings in recent years," the society's head of rights Richard Combes said.
"Consequently many are no longer able to sustain a career. The one truly irreplaceable link in the value chain is being stretched to breaking point."
Analysis: Will Gompertz, arts editor
There is a paradox for an author in 2015. It is harder than ever to make money from writing. And yet there are more people writing and publishing books than ever before. The market is reasonably stable but it can't begin to accommodate the hundreds of thousands of new books flooding it every year.
You don't have to be a maths scholar to work out the financial ramifications. Nor the consumer response. Readers, with little spare time are overwhelmed by the choice and end up sticking to what the authors they already know and trust.
Hence the big brand authors trade even better in an overcrowded market. Which is why literary prizes are so important. They provide a platform for new writing and an endorsed product on which time- poor punters can take a risk.
While a typical full-time writer earned £11,000 a year in 2013, the top 5% each earned at least £100,100, the research showed.
The report said: "Thus, it appears that writing is a profession where only a handful of successful authors make a very good living while most do not."
Around one in six writers did not earn any money from their writing in 2013, it said - despite 98% saying their work had been published or used in other ways.
And 11.5% of authors now earn a living solely from their writing - down from 40% a decade ago.