[GeneralMaximus]

While everything tastes better with ghee, you can cook a lot of Indian food using plant-based oils. I use sunflower oil for a lot of dishes, but you can also use vegetable oil, olive oil, or mustard oil.

With a bit of effort, you can eliminate animal products from most vegetarian Indian food. It will taste different, but not too much.

Source: I'm Indian.

[bluntfang]

I don't think anyways arguing that oil isn't a replacement for butter. I think we're curious about the expectation. Can we expect most Indian restaurants or caterers to use oils instead of ghee? Do you need to ask them if they use ghee?

[GeneralMaximus]

Fancy Indian restaurants in the West as well as back here are almost certainly using ghee. Cheaper places might use vanaspati (a ghee substitute made with palm oil) or oil. In general, though, you can never tell for sure unless you're doing the cooking yourself.