China's infamous outdoor “marriage markets” may be associated with desperate parents seeking life partners for their children, but public parks around the country are now becoming hotbeds for huanghunlian (黄昏恋), or “twilight love.”

Usually divorced or widowed, the parties to these aged, amorous arrangements flout yet another taboo in China: unmarried cohabitation. Some 20 percent of couples aged 18 to 60 are “living in sin,” according to a survey by Renmin University emeritus professor Pan Suiming, while around 59 percent have no plans of getting hitched.

Some couples cohabit for convenience—splitting rising rental costs, for example—or companionship, especially the so-called “twilight” twosomes. For others, it’s a case of coitus non-interruptus: Pan’s survey suggest a high level of sexual satisfaction among young cohabitees, compared to married couples. A 2005 global survey by condom manufacturer Durex found that 70 percent of married Chinese were disappointed with their spouse’s performance, and 44 percent did not discuss their needs, making Chinese among the “shyest lovers in the world.”

Of course, cohabitees could have it much worse—up until 2001, it was illegal under marriage law for a couple to live together without the legal formalities of marriage. Even today, if one or both partners are still married to another, cohabiting remains illegal. Still, 3.5 percent of Pan’s married respondents admitted to violating this law.

Live-in relationships unfettered by the bonds of traditional marriage might sound attractive to some, but lack of legal protections or social benefits are likely to hinder the idea from going mainstream—for now.