For a look at oil-at-ease, drive 40 miles north of Tulsa on Highway 123 to Woolaroc (918-336-0307), the country retreat of Waite Phillips's older brother Frank, founder of Phillips Petroleum Company. A child-pleaser, the 3,600-acre ranch is a combination of museum, historical lodge and drive-through wildlife refuge. Picnic tables, sometimes with a view of a buffalo herd, are provided. Woolaroc is open 10 A.M. to 5 P.M. Tuesday to Sunday. Admission is $2. Events

The Tulsa State Fair (Expo Square; 918-744-1113), Sept. 28 to Oct. 8, is one of the largest in the nation. Apple-pie judging and livestock shows compete for attention with the glitzy midway and entertainment including a professional rodeo as well as a horse show of primarily Western-style events. There are 10 acres of animal barns - beef cattle, sheep, swine, dairy goats and pygmy goats among them - including a petting barn with a variety of farm animals that can be seen up close. Admission is $4. Horse racing makes its debut this year with a two-week season (Sept. 16 to Oct. 1) at the new Fair Meadows Race Track, on the fairgrounds. Admission is $2. Post time is 1 P.M. daily.

Tulsa's Hispanic community turns the Williams Center Green downtown into a fiesta Sept. 14 to 17 with free entertainment daily including performances of salsa bands, Latin jazz fusion bands, gaucho singers from Uruguay and folkloric groups from Venezuela. Also part of the fiesta is an art exhibition at the University of Tulsa. Information: 918-596-7979. Getting Out

River Parks, Tulsa's most popular recreation spot, is a continuing festival. With 15 miles of trails along the Arkansas River, the park attracts joggers, bicyclers, walkers and weekend picnickers. Bicycles may be rented for $3 an hour at River Trail Bicycles (41st Street and Riverside Drive; 918-743-5898). The park also is the setting for many special events including the Great Raft Race (Sept. 4) when thousands of landlubbers watch strange craft float the Arkansas; Oktoberfest, Oklahoma's largest free festival (Oct. 20 to 22), and the Tulsa Run, a 15-kilometer race that attracts 12,000 runners.

The cooler weather brings out the best blooms at the Tulsa Muncipal Rose Garden (Peoria Avenue and 23d Street; 918-747-2709). The elaborately terraced, Renaissance-style garden displays 9,000 roses and is one of 22 sites in the country used to test and evaluate roses. It's open daily from 6:30 A.M. to 9 P.M. Nearby is another boom-era Italian villa mansion, now the Tulsa Garden Center (2435 South Peoria; 918-749-6401). The center (with its elegant conservatory and seasonal displays) is open to the public Monday through Friday from 9 A.M. to 4 P.M.

Creek Nation Bingo (1616 East 81st Street; 918-299-0100), owned by the Creek Indian Nation, draws busloads of gamblers to its 1,200-seat hall for the chance to win high-stakes pots of up to $100,000 a game. Cost of a session, which includes 14 games, begins at $20. Games are played every afternoon and Monday to Saturday nights. Where to Stay

The Westin Hotel-Williams Center (10 East Second; 918-582-9000) is in the heart of downtown, across from Tulsa's Performing Arts Center. A room for two is $140 Monday to Thursday, $54 Friday to Sunday.