Engine oil make for cars

Are all the lubricants of the different brands are same given the API spec say 20/40W.
Some companies say there oil is better than others and common man like me doesn't know about what they say and have no time to do R&D on this.
Since engine oils are costlier , any light on this subject.?

There are many engine oils available around, Castrol for Eg.

VT

Motul is the best oil you can use.period.

buddy, different manufacturers make engine oils, all according to the same spec. it has to be the same spec. maybe some companies use 'extra additives' in their oils & hence charge more.

most manufacturers set up a lubrication chart of all oils that can be safely used with their engines.
Stick with this and you'll be fine. there are even options of changing over to synthetic oils should you want that.
Bear in mind that although synthetic oils are much superior, the extended schedule of oil renewal should be adjusted to ambient and local conditions. e.g. the skoda octavia uses synthetic oils but instead of changing the oil at 30,000kms as is the normal schedule, they insist that you change it at 7500kms , then extend to 10,000kms and then finally to 15,000kms after crossing 100,000kms.
Please also bear in mind that there should NEVER be any metal particles in your oil/oil sumps - metals never touch each other, it's the film of oil that prevent them from doing so.
Ambient conditions such as high moisture have a tendency of affecting the quality and specs of the lub oil and therefore need to be considered, there is no set formula to calculate the reduction in oil change schedule based on high moisture content of ambient air and therefore only your manufacturer (who has carried out extensive tests in your region) can help.