Pay attention the geography of the tree. Oak trees grow in every region of Texas, and they tend to be near riverbanks in alkaline limestone soil. Some varieties, like the bur oak, might be nearer to the coast because they tolerate salty soil and sea spray.
Consider how much moisture the tree might get from natural precipitation. Most Texas oak trees are drought-tolerant, although some types, like the shumard oak and the water oak, fare better in moister soil.
Estimate the height of the tree. Oak trees in Texas range from medium to very tall, with heights between 50 and 120 feet. The widths of Texas oaks are varied as well, from the relatively narrow, 30-foot wide chinquapin oak to the sprawling live oak, which can be up to 100 feet wide.
Feel the bark of the tree. Most oak trees have rough textured or scaly bark that is gray or brown, but the shumard oak tree occasionally has smooth gray bark.
Look at the flower buds (called catkins) of oak trees in the spring. The catkins on oak trees are generally 1 to 4 inches long. Most oaks have green catkins, but the live oak's are yellow, the shumard oak's can be brown, and the Texas red oak has reddish-brown catkins.
Examine the leaves of the tree. Oak trees' leaves are quite varied from each other. The chinquapin has oval leaves with fringed edges, while the bur oak has very large leaves with multiple smooth lobes. Shumard oaks and Texas red oaks have deeply notched, pointed lobes, with four points on the shumard's leaf and six points on the Texas red's. The water oak has a bell-shaped leaf that is uncommon in oak trees.
Check the fruit when it appears in late summer and early fall. Oak trees produce acorns which drop in mid to late fall. Most acorns are brown or reddish brown, and about an inch in diameter. The bur oak has one of the largest acorns, reaching 2 inches in diameter with a fuzzy cap.
Look at the fall foliage. Most oak leaves change color before dropping off in late fall. The shumard oak is especially well-known for its stunning crimson leaves, although the chinquapin's yellow leaves and the Texas red's orange foliage really stand out.
Watch the tree in the winter months. While most Texas oak trees are deciduous, the water oak often keeps its leaves long into the winter, and sometimes doesn't lose them at all. The live oak is almost always evergreen in most climates.