The authors will also share in any money from eventual paperback sales.

In 1976, 81 per cent of total American paperback sales were controlled from eight large houses.

Sales to foreign publishers or paperback sales could offset some of that cost.

Royalties generally range from 7 percent to 8 percent of paperback sales.

The original hardcover edition eventually sold over 600,000 copies, and paperback sales exceed three million by 1984.

"So this milestone has come even sooner than we expected - and it's on top of continued growth in paperback sales."

Total paperback sales, which came to about $120 million in 1991, reached $165 million in 1994.

But multi-million paperback sales have become increasingly rare, in part because of the big discounts for hardcover books.

Each book would earn that author around £50-100,000 in its first year of release at traditional royalty rates, with paperback sales still to come.

Little, Brown plans to start publishing mass-market paperbacks, even though overall paperback sales are declining.