Well, personally, I've always done very well in early July. Used to always go there on the 4th of July weekend through HS and college. Here are all of my July Oil Creek outings back to 96, from my journal.
Friday, July 5, 1996: Fished Oil from 5 p.m. till dark. Caught 16, including 2 in the mid-teens. All browns on minnies.
Saturday, July 6, 1996: Fished Oil all day, with a break for lunch. Landed 36 fish, mostly browns on minnies, but also some rainbows on eggs.
Friday, July 4, 1997: Fished Oil in the morning, 8 fish before lunch. All 3 species caught, surprised to catch brookie in Oil.
Friday, July 3, 1998: Fished Oil all day. Skunked! There was a hatch on, fish rising everywhere, but wouldn't take bait. A fly fisherman at the parking area said he caught 21 that day.
Saturday, July 4, 1998: Took dad's old fly rod to Oil. No hatch, no risers. Bait fisherman nearby cleaned up. Frustrating, tons of fish here and I can't get em.
Sunday, July 5, 1998: Took both the spinning rod and the fly rod, tricky to ride the bike with 2 rods and a minnow bucket. Caught 1 fish on mealworm in morning, then hatch started. Must of had 50+ hits on dry flies, every frickin cast. Only hooked (and landed) one, on a white bug of some sort. My first fish on a fly rod! Hatch ended around 11 a.m. and I switched to spinning rod till dinnertime, and ended up with 27 fish on the day.
Friday, July 7, 2000: Fished Oil from 2 p.m. till dark. Caught 18, mostly browns working live minnows across the flats.
Saturday, July 14, 2001: Fished Oil from 7 a.m. till around noon. Caught 9 trout and a bass on streamers, fishing died off after 10 a.m. Dad got 14 on live minnows, all trout.
Saturday, July 6, 2002: Fished Oil from 2 p.m. till 7 or 8, when I was chased off by a thunderstorm. 12 fish caught, mostly rainbows on egg imitations in deeper faster runs.
Sunday, July 20, 2003: Fished Oil all day. Fishing tough, but managed 6 browns on live minnows. Dad got 3 browns and 2 smallmouths.
Monday, July 13, 2009: Fished Oil in the evening. A few sulphur spinners, and a fair amount of egg laying caddis. Skittering a stimmie at dark was nuts! Landed 9, all of them in the last hour.