Verdict: Ontario coloured-fuel enforcement runs as administrative reassessment plus POA tickets, not as criminal prosecution. The deterrent for a farmer or fleet operator is the audit (7-year records, 3×–10× tax penalty, up to 13× tax administrative penalty) — not the courtroom.

What the Ministry's published material says

Two Ministry pages frame the enforcement posture:

• Ministry of Finance Inspectors (ontario.ca/document/gasoline-tax/ministry-finance-inspectors): "Inspectors sample the fuel tanks of diesel vehicles under the coloured fuel program to identify operators who may be avoiding fuel tax … Inspectors conduct regular visits to locations with fuel storage facilities, bulk plants, and service stations to ensure taxes have been paid on products used in licensed vehicles and to detect any misuse of tax exempt product."
• IFTA inspectors operate marked enforcement vehicles with emergency lights and "take samples from fuel tanks of diesel vehicles."

Audit triggers (publicly identified)

The Ministry of Finance lists these red flags in the "Attention Truckers" pamphlet and "Coloured Fuel" overview:

• Mixed coloured/clear in a single tank. "Mixing coloured fuel with clear fuel will not produce a larger volume of usable product. Instead, it will make the entire quantity unsuitable for use in a licensed motor vehicle."
• Tanks not labelled with the Ministry-issued coloured-fuel labels and tags.
• Receipts inadequate for the seven-year retention requirement.

The Ministry does not publish specific volume-vs-fleet-size thresholds, rural/urban patterns, or other quantitative audit-trigger criteria. Audit triggers beyond the above are confidential.

Where dip tests happen

• Roadside: licensed-vehicle dip-test by Ministry inspector or in joint operations with MTO/OPP. Inspectors use marked enforcement vehicles.
• Farm-show parking lots and agricultural events: community evidence (AgTalk thread tid=278064) confirms inspectors target large gatherings of farm trucks. "A large gathering of farm trucks, like a sale [or] big ag event" is a common venue.
• Bulk plants, service stations, fuel storage facilities: scheduled and unscheduled site visits.
• Audit reassessment: post-fact, on records — the seven-year retention obligation makes a paper audit possible without any in-person inspection.

Court record (or lack of it)

A targeted CanLII search of Ontario Court of Justice and Tax Court of Canada decisions for the 2020–2026 window found no reported decision involving a farmer, custom operator, or trucker for coloured-fuel misuse. Two reasons:

1. POA-level convictions are not indexed on CanLII. Set fines under the Provincial Offences Act are typically not reported as judicial decisions.
2. Most enforcement is administrative reassessment — a Ministry-issued Notice of Assessment plus penalty, with the taxpayer's recourse being a Notice of Objection under FTA s. 28 / 29, not a criminal prosecution.

The absence of CanLII decisions is not evidence of low enforcement. The Ministry's audit and reassessment activity continues; it just doesn't produce judicial decisions to read.

Auditor General context

The Auditor General of Ontario has not audited the Ministry of Finance Fuel Tax / Gasoline Tax program in the 2020–2026 window. The most recent AG product on this program is the 2010 audit with its 2012 follow-up (auditor.on.ca). The AG's May 12, 2026 special-report release (Family Responsibility Office; Large Commercial Truck Driver Licensing; Special Education; AI in Government — Newswire.ca, "Ontario Auditor General Releases Four Special Reports," 12 May 2026) contains no coloured-fuel content.

Ontario does not publish dip-test counts, audit volumes, or revenue recovered for the coloured-fuel program. Enforcement posture has to be inferred from Ministry pages, trade-press coverage, and community evidence.

"Attention Truckers" pamphlet — provenance note

The pamphlet has no revision date in either of its two published Ontario.ca / fin.gov.on.ca locations. The internal $440 fine value is the only dating signal; the Coloured Fuel overview page lists $465. See Coloured (dyed) diesel — Ontario eligibility, recordkeeping, and penalty ladder for the discrepancy treatment. The pamphlet remains the canonical Ministry message on roadside dip tests, examination of farms and truck yards, and the penalty ladder.

Trade-press coverage 2020–2026 (limited)

• Farmtario, Increasing enforcement coming for farm vehicles using Ontario roads (farmtario.com/machinery/increasing-enforcement-coming-for-farm-vehicles/) — the article covers SMV signage, lighting, 4-way flashers, farm-plate scrutiny. No dyed-fuel content.
• Farmtario, Crime proof your farm by design (farmtario.com/news/crime-proof-your-farm-by-design/, 2025) — Discusses on-farm fuel as a theft target, not as a dye-misuse risk.

No trade-press audit case of a custom operator over coloured fuel was located in the 2020–2026 window.

Sources & structured attribution

• source.document: Ontario Ministry of Finance, Coloured Fuel bulletin (ontario.ca/document/fuel-tax/coloured-fuel); Attention Truckers pamphlet (fin.gov.on.ca/en/bulletins/ft/pamphlet_truckersdyeddiesel.html and ontario.ca/document/fuel-tax/attention-truckers-no-dyed-diesel-highway); Ministry of Finance Inspectors (ontario.ca/document/gasoline-tax/ministry-finance-inspectors); Auditor General of Ontario, 2010 audit and 2012 follow-up, plus 2026 May 12 special-report announcement (Newswire.ca); CanLII targeted search 2020–2026 (no reported decisions located); AgTalk thread tid=278064 (farm-show parking-lot enforcement, community evidence); Farmtario coverage (farmtario.com)
• source.section: Inspectors page; Coloured Fuel red-flag list; Attention Truckers pamphlet; CanLII negative finding
• source.captured_date: 2026-05-13
• source.confidence: verified (Ministry pages; AG record; CanLII negative finding); inferred (community-evidence venues like farm-show parking lots are corroborated by single-thread reports rather than Ministry confirmation)
• concept_category: regulatory compliance / fuel tax / enforcement
• applies_to_services: dyed-diesel sales; clear-diesel sales; bulk-plant operations; customer audit support
• applies_to_audiences: farm, fleet-commercial, construction customers facing audit risk

Confidence: verified.