Can I use a gas grill to cook a 4lb standing rib roast. How long do I keep it on the grill?

Turn both sides of your grill on high for about 10 minutes and get it good and hot. Then sear the roast a little on each side. After this, turn one side of the grill completely off and leave one side on med to med high. Move the rib roast to the off side and let it sit in the with the lid closed for about 3 hours (depending on your grill that would make it about medium to medium well). I've done this many times and gotten rave reviews!

I wouldn't cook that fantabulous cut of meat on the grill; it benefits from self-basting and being surrounded by dry heat in the oven. That said, temperature is what ur after. I usually shock the roast at 500 degrees for 15 minutes then 20 minutes per pound at 350 degrees. So on a grill you will need a surface thermometer and use the times as a guide.

Hope this helps.