...that the Corleone family was getting out of the Olive Oil business and into Casinos? Did they really deal in Olive Oil or was that a euphemism for racketeering?

They really did... remember how that was Vito's legitimate business?

I wasn't aware that there was such a demand for olive oil to establish a family fortune.

Well, Sonof70s, Micheal was leaving the olive oil business, but I doubt that is what he was really talking about. He was pretty much summing up that all of New York business would be over.

The olive oil business was the "legitimate" cover for the Corleone family rackets: gambling and unions. When Michael said the family was leaving the olive oil business, he meant that they were quitting New York and relocating their operations to Nevada to the (legitimate)casino business. But, as we saw in GFII, complete "legitimacy" had eluded Michael.

Just and extension on what Turnbull said. Since the Olive Oil business was at a time at least the largest importer in the US, it would have been a great front for money laundering since you could launder more money with a larger business than a smaller one, naturally.