Silly Oil Question

[dpg]

I've got 4.5 quarts of one particular brand of synthetic oil and I cannot find another new quart of the same kind (brand.) Would it be ok to top off the half quart with another brand synthetic of the same weight and just use it for an oil change in my car? It's Shell and I've been to two stations, Wally Mart and an auto parts store None have the exact thing I'm sitting on.