The council said that it studied over 207 hours of scripted shows on the five main American broadcast networks, and found that spoken references to non-marital sex outnumbered mentions of marital intimacy by about three to one.
The ratio was four to one for scenes that visually depict or imply sex, said the council.
The study showed once-taboo topics like partner-swapping, threesomes, strippers and prostitution were increasingly becoming common these days.
"(TV networks) are more interested in being shocking. They're more interested in being provocative than telling a story that's going to resonate with the vast majority of TV viewers," the Sydney Morning Herald quoted Melissa Henson, the study's author, as saying.
The four-week study of programs on ABC, CBS, Fox, NBC and CW networks discovered 151 verbal references to non-marital sex and 54 to married sex.
It also revealed that marital sex was often described in a boring or disrespectful way whenever it was mentioned on TV.
"(Prime-time TV) seems to be actively seeking to undermine marriage by consistently painting it in a negative light," Henson said.
The PTC said that the ABC network, part of the Walt Disney empire, had most sexual references, particularly to adultery.
Although ABC would not comment on the PTC study, an advocacy group backed in part by the entertainment industry said that it was biased, faulty and designed to influence legislators and raise money.
Jim Dyke, executive director of TV Watch, said: "The Parents Television Council won't be satisfied with television content until they convince the Government to enforce their personal, selective judgements."
He even said that the study supported the belief that "parents aren't competent enough to make television viewing decisions for their own families."