When a refinery goes offline unexpectedly, it certainly does create a disruption in supply. Refineries so affected have to very quickly scramble for makeup supply, which they will achieve by importing from the United States, bringing in product from other regions, often by rail, or borrowing from their next door neighbours within the same region. I've never seen a case of cars stranded on the 401 for lack of being able to get gasoline. Although we certainly have, in Canada, witnessed rotating closures of gas stations as a result of these shortages, generally they have been associated with the early stages of these supply disruptions before makeup supply could be put in place.
The fact is that certainly up until 2008, the consequences of unexpected supply disruption, whether it's refinery or pipeline, have created problems. With supply capacity now being a little further removed from actual demand, the consequences are not as severe as they used to be. Although that has an effect on crack spreads, making them not as attractive for investment as when refinery capacities are running at full, I really don't see that as being a problem, with spare capacity being available now.