Is there a rule that creates a presumption of agencywhen a person who owns a car permits another to drive it-either on a regular basis (like a son or a girlfriend of the owner) or on an irregular basis (say one allows a friend to borrow his car to go to the barber shop or golf course). In the case I have in mind there is no benefit derived by the owner.

Answer: Here are your cases:
Automobiles - Agency - Presumption Driver is Owner's Agent

Norton v. Harmon, 1942 OK 391, 133 P.2d 206, 209-10: Recognizes presumption; accord: Stumpf v. Montgomery, 1924 OK 360, 226 Pac. 65; Hintergardt v. Operators, Inc., 940 F.2d 1386 (10th Cir. 1991): Owner may rebut presumption by preponderance of evidence; accord: Pollard v. Grimes, 1949 OK 225, 210 P.2d 778, 781.

There's a related presumption of permissive use which other states recognize, but I'm unaware of an Oklahoma case on it. See McKirchy v. Ness, 256 Iowa 744, 128 N.W.2d 910, 911 (1964): Driver is presumed to have permission to drive the car. Accord: Fout v. Dietz, 401 Mich. 403, 258 N.W.2d 53, 54 (1977); contra.: State Farm Mut. Auto Ins. Co. v. Eakins, 748 So.2d 765 (Miss. 1999); Marquez v. Enterprise Rent-A-Car, 53 CalApp.4th 319, 61 Cal.Rptr.2d 557, 558 (1997), Washington v. State Farm Mut. Auto. Ins. Co., 709 So.2d 360, 362 (La.Ct.App. 1998