"Both have been picked up, both will be ready for work, and we'll work it out," he said.
The network announced that it was picking up options on both women's contracts, which would require each to return to the show that has featured them mixing with everyday folks while they work their way across America.
Asked what direction the fourth installment will take, Liguori said that hadn't been determined yet. But both women recently have become engaged, so a show focusing on their wedding planning might be in the works, he said.
"Given the fact that both Paris and Nicole are engaged and about to be married ... there's got to be something in that world," said Liguori.
No airdate has been set for The Simple Life 4.
When Paris Hilton and Nicole Richie's relationship took a nosedive last spring, the future of the socialite duo's popular reality show was up in the air. The chemistry worked fine for the show's first three outings, until a public falling-out between the onetime buds led Hilton to issue a statement that she and Richie were "no longer friends."
Although there was rampant speculation as to what Richie did that so offended her friend, Hilton merely said, "Nicole knows what she did, and that's all I'm ever going to say about it."