Oklahoma Plumbing Contractor and Natural Gas Exam: Complete 2026 Prep Guide
You've put in the hours on job sites, learned the trade, and now one exam stands between you and your Oklahoma plumbing contractor license. The Oklahoma Plumbing Contractor and Natural Gas exam is challenging — 85 scored questions covering everything from vent sizing to isometric pipe calculations — but it's absolutely passable with the right preparation. This guide breaks down exactly what's on the exam, what books you need to bring, how to study efficiently, and how to start practicing today. Ready? Let's get into it.
Oklahoma Plumbing Contractor and Natural Gas Exam Overview
The exam is administered by PSI and consists of 85 scored questions completed in 180 minutes (3 hours). To pass, you need to answer at least 75% correctly — that's 64 out of 85 questions.
Here's what makes this exam a little different from most: it's open book. You bring your own approved reference materials to the testing center. That sounds like a huge advantage, but don't let it lull you into underestimating the prep required. The exam is timed, and fumbling through unfamiliar code sections is a fast way to run out of the clock. Fast, accurate navigation is the real skill you're building.
You can register for the exam through PSI once the Oklahoma Construction Industries Board has approved your application. Visit the exam registration page to schedule, or call PSI at (855) 834-8750. You'll need the OK Con ID number the Board provides to complete registration. For full candidate details, check the official exam bulletin.
What Topics Are Covered?
The exam spans ten topic areas. Here's how the 85 scored questions break down — and where to focus your energy:
- Vents (13 items) — The single heaviest topic. Vent sizing, developed length, termination rules, air admittance valves, wet vents, circuit vents, and more.
- General Plumbing Knowledge and Regulations (10 items) — IPC Chapter 1 scope, permit requirements, inspection types, and pipe length calculations.
- Water Supply (10 items) — Backflow prevention, pipe sizing, cross-connection control, and valve requirements.
- Drains and Sewers (10 items) — Pipe materials, fixture unit sizing, horizontal drain slope, cleanout rules, and below-grade systems.
- Traps, Interceptors, Indirect, and Special Waste (10 items) — Trap dimensions, grease interceptors, oil separators, indirect waste piping, and air gap vs. air break.
- Piping, Valves, and Control Valves (8 items) — Pipe joints, approved materials, pressure-reducing valves, backflow preventers, and support spacing.
- Fixtures and Equipment (8 items) — Minimum fixture counts by occupancy, installation clearances, water heater safety devices, and flushing controls.
- Isometric Analysis (7 items) — Reading isometric diagrams, center-to-center and end-to-end calculations, 45° offset constants, and fitting allowances.
- Fuel Gas (5 items) — Gas pipe sizing methods, approved materials, pressure drop, appliance venting, and combustion air.
- Safety (4 items) — Fall protection, guardrails, ladder safety, and personal protective equipment.
Vents alone account for more than 15% of the exam — start there.
Sample Questions
Here are a few questions representative of what you'll see on the Oklahoma plumbing contractor exam. Read through them — and see if you can figure out the right answers before looking them up in your code books.
Question 1 — Vents (Easy)
Every dry vent connecting to a horizontal drain must connect at what position relative to the drain pipe?
- A) Below the centerline of the horizontal drain pipe
- B) At the invert of the horizontal drain pipe
- C) Above the centerline of the horizontal drain pipe
- D) At any point on the circumference of the horizontal drain pipe
Question 2 — Drains and Sewers (Medium)
What is the minimum clearance required from the face of a cleanout opening to any obstruction for piping 8 inches and larger?
- A) 18 inches
- B) 12 inches
- C) 36 inches
- D) 24 inches
Question 3 — Drains and Sewers (Medium)
Where a horizontal drainage pipe has a change of horizontal direction greater than 45 degrees, a cleanout is required at the change of direction. If multiple such changes occur within a certain developed length, one cleanout may serve all changes within that length. What is that developed length?
- A) 50 feet
- B) 40 feet
- C) 30 feet
- D) 20 feet
Question 4 — Safety (Easy)
How often must safety nets be inspected for wear, damage, and other deterioration?
- A) Daily
- B) Every two weeks
- C) Monthly
- D) At least once a week
Question 5 — Piping, Valves, and Control Valves (Easy)
You are a plumbing contractor installing a new water distribution system using galvanized steel pipe. When making threaded joints, where should pipe-joint compound or tape be applied?
- A) On both male and female threads
- B) On the female threads only
- C) On the male threads only
- D) Neither; threaded joints on galvanized steel do not require compound or tape
Not sure on a few of these? Take our free practice exam to test your knowledge — no account or payment needed.
What Types of Questions to Expect
Our Oklahoma plumbing contractor exam prep bank includes 615 practice questions covering all ten exam topics. Here's what each area tests:
- General Plumbing Knowledge and Regulations: IPC scope and applicability, permit procedures, code official authority, required inspection types, and pipe length calculations using fitting allowances for threaded, copper, and PVC.
- Piping, Valves, and Control Valves: Joining methods for gas and water piping, approved pipe materials and standards, valve types and required locations, center-to-center vs. end-to-end measurements, and support/hanger spacing.
- Fixtures and Equipment: Minimum fixture counts by occupancy type, installation clearances, individual fixture requirements (water closets, showers, urinals, sinks), flushing devices, and water heater safety device rules.
- Water Supply: Backflow prevention devices and their application, pipe sizing for flow rates and pressures, cross-connection control, potable water protection, and shutoff/pressure-reducing valve placement.
- Drains and Sewers: Sanitary drainage pipe material selection (above-ground and underground), fixture unit values and sizing tables, drain slope requirements, cleanout location and spacing rules, and sump/ejector systems.
- Vents: Vent pipe sizing and developed length calculations, vent terminal heights and clearances from openings, every major venting method (wet, circuit, island fixture, single-stack), air admittance valve rules, and dry vent connection requirements.
- Traps, Interceptors, Indirect, and Special Waste: Fixture trap dimensions and prohibited types, trap seal depth and protection, grease interceptors and automatic grease removal devices, oil and sand interceptors, and indirect waste piping with air gap vs. air break distinctions.
- Isometric Analysis: Reading isometric drawings to calculate c-c and e-e pipe lengths, applying the 1.414 diagonal multiplier and 0.707 offset multiplier for 45° offsets, three-pipe offset diagrams, and fitting allowances for threaded, copper, PVC, and cast iron.
- Fuel Gas: Gas pipe sizing using longest-length and branch-length methods, approved materials (steel, CSST, polyethylene, prohibited materials), pressure drop limits, appliance vent sizing and termination, and combustion air requirements.
- Safety: The 6-foot fall protection trigger, personal fall arrest system components, guardrail specifications, ladder safety and inspection, and PPE selection for head, eye, face, foot, and hearing protection.
Required Study Materials
Because the exam is open book, these aren't optional — you need to own, tab, and know how to use all four references before test day:
International Plumbing Code (2018) — The backbone of the exam. Most questions on vents, drains, traps, fixtures, and water supply trace directly back to the IPC. Get familiar with every table you'll need for sizing.
2018 International Fuel Gas Code (IFGC) — Covers the Fuel Gas topic area. Gas pipe sizing tables, appliance venting, and combustion air requirements all live here.
Mathematics for Plumbers and Pipefitters (8th Edition) — Essential for the Isometric Analysis questions. If you're rusty on 45° offset math or fitting allowance calculations, work through this book before exam day.
OSHA 29 CFR 1926 — Covers the Safety topic. Fall protection, guardrails, ladder requirements, and PPE rules are all pulled from this reference.
Bring your Oklahoma-revised editions of the IPC and IFGC if available. The state licensing website and the official exam bulletin have the most current information on approved editions.
Study Tips for the Oklahoma Plumbing Contractor Exam
Give yourself three to six weeks. Use the Candidate Information Bulletin as your roadmap and spend your time building find-it-fast skills rather than memorizing code sections word for word. On a timed open-book exam, the contractor who can flip to the right table in 20 seconds beats the one who tried to memorize everything.
Set your practice target above the cut score. Aim for 80% or higher on practice runs — not 75%. That buffer is what keeps a few tricky questions from sinking you on test day.
Work every question once, then come back. Answer what you know, flag what you don't, and move on. Burning five minutes on a single vent calculation while other questions sit unanswered is a losing strategy. Our practice exams let you bookmark questions for review, exactly like the real exam interface.
Tabbing your books is worth the time. Permanent tabs are allowed; sticky notes like Post-It tabs are not (they must be removed before the exam starts). You may highlight and underline, but you cannot write notes in the margins before or during the exam.
Manage test anxiety with a simple reset. A little nervousness is normal — acknowledge it and keep moving. If you feel stuck on a question, take a few slow breaths before forcing an answer. If your test center allows a break, use it — just remember the timer keeps running.
Start Practicing Today
The PSI Oklahoma plumbing practice test experience you build now is what carries you through on exam day. Start with our free practice exam — 10 questions, no account required, no payment. It's a fast way to gauge where you stand and get a feel for the question style.
When you're ready to go deeper, the full practice exam mirrors the real test: 85 questions, 180-minute timer, and the same topic breakdown — with detailed score reporting by topic so you know exactly where to focus. Every attempt pulls from a large question pool, so you won't see the same exam twice.
You've already done the hard work out in the field. Now it's time to prove it on paper. You can do this.