Ask Mr. Smarty Plants

Grapes are in the genus Vitis in the family Vitaceae, and there are numerous species and varieties of grapes grown in the United States. This link to okwildcrafting.com indicates at least 11 species growing in Oklahoma with the species Vitis acerfolia occurring in Ellis County.

Lets clear up a little terminology before we continue. If a plant species has flowers that contain both pistils and stamens, the flower is termed perfect, and the condition is termed monoecious (or hermaphrodite in some cases). In many cases the flowers can self pollinate. If a species have pistillate (female) flowers  on one plant and staminate (male) flowers on another, the condition is termed dioecious. In this situation you would need “male plants” and “female plants” in order to produce grapes.

A widespread species of wild grape is Vitis mustangensis (Mustang grape). Looking through this link to plantsforafuture.org, we find that the mustang grape is considered monoecious (both male and female flowers on the same plant).

If you look through this article from AgriLife Extension you will find this statement
“Wild grapevines, rootstocks (and a few cultivated varieties such as St. Pepin) have either pistillate (female) or staminate male flowers -- that is, the entire vine is either male or female. Vines with female, pistillate flowers need nearby vines with staminate or perfect flowers to produce fruit. The majority of commercial grapevine varieties have perfect flowers, that is, both male and female components.”
 
So the situation isn't as simple as one would like. The answer to the question then is to look at the flowers, and the AgriLife Extension article has some pretty decent photos of perfect flowers. When you examine the flowers from your vines, look for the stamens and the pistils;if they are both present, you have a perfect flower; if the stamens are missing, you have a female flower and thus a female plant. It may have produced grapes last spring. If you find stamens and no pistil you have a male. You will need a magnifying glass, or hand lens, to do your examination.

For some help closer to home, you msy want to contact the folks at the Eiils County office of Oklahoma Cooperative Extension Service.