Oil Gauge Shaking in a 1993 Buick Regal Custom?

I have a 1993 Buick Regal Custom. Lately, the oil guage needle has started to shake violently, particularly if the car is revved up (by depressing the accelerator). Its movement is towards the upper scale and many times past it; it does not go down below the indicateor where the oil level might normaly be.