Solo music by all four Beatles members is available online
"It's down to fine-tuning, but I'm pretty sure it'll be happening next year, 2008," he told Billboard.com.
The Fab Four are one of the last major acts to withhold their back catalogue from stores like iTunes and Napster.
Sir Paul said the delay was due to contractual issues and planning by all parties involved. "You've got to get these things right," he said.
"You don't want to do something that's as cool as that and in three years time you think, 'Oh God, why did we do that?'"
Sir Paul added: "There's just maybe one little sticking point left, and I think it's being cleared up as we speak, so it shouldn't be too long."
Albums by the late Beatle George Harrison were made available online last month, meaning solo music by all four band members can now be bought digitally.