how is oi calculated on options?, page-5

Open interest - coming back to the original question - is how many contracts are open at any given point in time. wih a delay of one day. e.g. if you made a transaction (let's say the only one in that series) today, it won't show up in tomorrow's Fin review, not till one day later. that's been my observation, haven't checked up on it lately, being of only academic interest.

I believe there is some regulation to ensure that the number of open option contracts must not exceed the number of shares on issue, but there again I'm on hazy ground.

from the practical viewpoint, you will find that where there are the most open contracts, is where you want to be looking to get in. mostly, they'll be reasonably close to the money, with a timespan of at least a couple of months to expiry.

people who tell you to apply stop-loss - similar to when you trade shares - have never traded options. when the underlying share goes against you, the option doesn't just move, it'll crash before you've got time to pick up the phone.

that's why some 80 or 90% of options expire worthless. because the poor sucker never had a chance to get out. in my own experience, well I've got to where it's more like 50/50. after a few decades of option trading, there is still room for improvement.