I had a good quality o-ring chain for around 20-25000kms, perhaps a bit more (I work in miles, but tthought I shoudl keep Norm happy!) Around 15000 miles or thereabouts. I replaced it with a cheaper option, non-o-ring. It lasted 6000kms (maybe 4000 miles) and needed adjusting every other week. I have since replaced it with an o-ring version again, not put many miles on it (maybe 1000-1500)... but haven't had to adjust it yet. Moral = pay more for a chain, it'll last longer if you maintain it, and cost you less in the long run
