Depends on who makes the engine.
After that, fill in the blank.

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=postlist&Board=14&PHPSESSID=

10-30 all the time. Pennzoil is good.

Mobile 1 synthetic. 10 W 30 after break in. Dino oil till then.

I use Briggs & Stratton straight 30 weight. In my mowers that don't have Briggs I use Castrol straight 30.

Briggs Stratton book says not to use multi-viscosity oils.

That must be an old Briggs & Stratton book. Their recommendation, for at least the last few years, gives a primary recommendation of synthetic 5W30 for all temperatures from -20 degrees to +120 degrees. They recommend straight 30W for temperatures above 40 degrees, and regular,non-synthetic 10W30 for temperatures up to 80 degrees. They sell a 5W30 synthetic oil under their own name brand.

Amsoil Formula 4-stroke for small engines.

Here is a link that might be useful: Amsoil

Yes, it is an old book, but all my mowers are old also, lol. So thats why I still use only straight 30. I guess the engines like it fairly well they are still running strong with no abnormal noises.

I'm not sure what information you are asking for. By kind of oil are you asking about weight, manufacturer, synthetic or non-synthetic or what?

For information about the oil to use in your lawn mower (not mine) I would refer you to the owners manual for your mahcine. It will likely give a range of weights that are appropriate for several temperature ranges. And it will likely tell you whether synthetic oil is recommended. Just follow the directions for your machine.

I use straight 30W also. The way I interpred the "new" recommendations as posted by xlindax, straight 30W is the correct usage for me. I never mow in temps below 40degrees, and summer temps above 80degrees are pretty ordinary around here, and the 30W non-synthetic is usually stocked even in the small-town autoparts and hardware stores.

I've heard of using synthetic oil when mowing rough terrain is a good idea? Found some good info at lmf too on this:

Here is a link that might be useful: synthetic oil in mowers

Castrol GTX 10-30 in all of them.

Castrol 30W in all small equipment. In big motors synthetics.

Whatever brand name 5W30 synthetic is on sale.