Just received a report today on market shares and this was the way it broke down.
USA Passenger Car Oil (includes pick-ups, etc)
1. Pennzoil
2. Quaker State
3. Valvoline
4. Texaco Havoline
5. Castrol
6. All the rest. This includes brands like Mobil, Conoco/Phillips, CITGO, and all the OEM oils.
USA HDEO:
1. Shell
2. Chevron
3. Mobil
4. All the rest
USA Industrial Lubricants: (paper mills, etc)
1. Mobil
2. Chevron
3. Shell
4. All the rest
Europe Passenger Car Oils:
1. Shell
2. Mobil
3. Castrol
Asia Passenger Car Oils:
1. Shell
2. Castrol
3. Mobil
Worldwide Shipping: (large freighters, etc)
1. Shell
2. Castrol
3. Cal/Tex
4. Mobil
Now to give you an example of size (volumes) in the USA. There is more Pennzoil sold than Quaker State and Valvoline put together. Depending on what market segment you are looking at, Pennzoil has anywhere from 29% to 44% market share.
Just enough to get my kid through college, after that I retire, then I don't care.