Subsurface Maps 750-1000 250-500 Figure 7. Cumulative oil production map for the a, B, c, and D Ector and crane counties, Texas. Contours in MSTB/year/acre. (After Major and Holtz, 1989)Subsurface Maps 299 >1000 750-1000 500-750 250-500 <250 Figure 7. Cumulative oil production map for the A, B, C, and D zones from the San Andres Formation reservoir, Jordan field, Ector and Crane counties, Texas. Contours in MSTB/year/acre. (After Major and Holtz, 1989.)