Oil companies are blocking research into the effect of spills of diluted bitumen into the sea, by keeping the composition of the diluent fluid secret.

I don't believe in prohibing companies from keeping secrets, not in general. But companies are not persons and they are not entitled to human rights. Any time their secrecy interferes with some public need, the state should require publication. The companies that don't like this are welcome to shut down or go away -- good riddance to them.