Diesel engine oil is usually OK for petrol engines there are two US spec numbers to look for I think US MIL 45162 for petrol and US MIL 2104D etc for diesel, as long as it has both no problem.
Thinner oils save a bit of fuel but as a classic commercial engineer I would go for a thicker variety, they save engines, there is a huge amount of codswallop about oil, any decent engine oil will do, in fact it is down to addatives most of which come from the secretive Lubrisol firm in Derbyshire, so whatever oil you get the addative pack will be similar, often it is the same oil sold between the majors.
A nice 10W/40 is always a good choice, buy the cheapest branded product you recognise. It is possible to run a modern engine on a decent quality washing up detergent (not recommended but will run)
Chris444
