I am not an expert in refining, but I do know that crude is sweetened at a refinery by mixing it with hydrogen with a catalist and taking the resulting hydrogen sulfide gas and removing the sulfur by freezing it so the sulfur drops out, or burning the hydrogen sulfide. All of this process is energy intensive-the hydrogen comes from natural gas. Gas prices are fairly low right now, but, as they rise will raise the refining costs. I haven't the slightest idea about how much gas is needed, but probably someone who knows can fill us in.