How do we know oil companies didn't cut production of gas to diminish it's supply just to hike up the prices?

Can we really be sure of what the internal affairs of company are? It may be unethical to artificially raise the gas prices based on a lie, but it doesn't mean that no one wouldn't do especially if they think they could get away with it. Insider trading and tax evasion are illegal but still happen from time to time. Look how money the oil companies are making with all the raised gas prices?