Diesel engines really can run on vegetable oil, Rudolf Diesel really did think that mattered, and hemp oil really was a lamp fuel before petroleum. Every step of the popular version overstates one of those facts — and the biggest claim built on them, that hemp could replace fossil fuels, is an activist argument from the 1980s that the numbers do not support.
Historical and technical material concerning industrial hemp seed oil, not cannabis flower. Nothing here is legal or engineering advice.
1. What Diesel Actually Did and Said
The claim in hemp literature is that Rudolf Diesel’s engine (German patent filed 1892, granted 1893) was designed to run on vegetable oil. That is not what happened, and Diesel’s own account settles it.
Diesel gave that account in his 1912 lecture “The Diesel Oil-Engine” to the Institution of Mechanical Engineers in London, published that year in Engineering (vol. 93) and in the Proceedings of the Institution of Mechanical Engineers. All the quotations and the Paris account below come from that 1912 paper.
The engine was built for mineral oil. In Diesel’s words: “The engine was constructed for using mineral oil, and was then worked on vegetable oil without any alterations being made.”
The famous demonstration was not his. At the 1900 Paris Exhibition the Otto Company showed a small diesel engine running on arachis (peanut) oil, at the request of the French government. Diesel described this in 1912; he was not the one who did it.
Peanut oil, not hemp oil. Every version of this story that reaches cannabis literature substitutes hemp for peanut. There is no documented hemp-oil demonstration.
But Diesel’s own view is the interesting part, and it is more prescient than the mythologised version:
“The fact that fat oils from vegetable sources can be used may seem insignificant to-day, but such oils may perhaps become in course of time of the same importance as some natural mineral oils and the tar products are now.”
In the same paper he noted practical advantages: the oil worked almost as well as mineral oil, could double as lubricant, and could be produced on the spot. He also argued that when fossil reserves were eventually used up, motive power could be produced from the heat of the sun.
That is a serious 1912 argument for locally produced biofuel and energy independence, made by the engine’s inventor. It does not need hemp added to it to be remarkable.
2. Lamp Oil, Before Petroleum
The other historical claim in Jack Herer’s The Emperor Wears No Clothes is that before 1800, hemp seed oil was the world’s most widely used lighting fuel after whale oil.
The general picture is right. Before kerosene, lighting ran on whale oil, tallow, and a range of vegetable oils — and hemp seed oil was among them, particularly in regions where hemp was already grown for fibre and the seed was a by-product.
The ranking is not something we can verify. “Most popular after whale oil” is a global claim about pre-industrial fuel use that would require data nobody collected. Treat it as unverified; the defensible statement is that hemp seed oil was one of several vegetable oils used for lighting where hemp was cultivated.
And it lost to kerosene on the merits, decades before any prohibition — the same pattern hemp followed in paper, textiles and the rope and canvas of the age of sail. Petroleum distillates were brighter, cheaper and more plentiful. That is the whole explanation.
3. The Energy Claim, Checked Against the Numbers
Herer’s larger energy argument in The Emperor Wears No Clothes — that hemp could replace fossil fuels, reverse the greenhouse effect and save the planet — is an activist position from the 1980s and 1990s, presented as a policy conclusion. Its core was not seed oil but whole-plant biomass: grow hemp for its stalks and leaves, then turn the dry matter into charcoal, methanol and fuel gas by pyrolysis. It was not derived from an energy analysis, and it should be read as the advocacy it is.
Two reasons it does not survive.
Biomass versus demand. Hemp is a good biomass crop. European field trials report roughly 6–16 t of dry matter per hectare depending on year, site and variety. A Lund University study put hemp’s gross biomass energy yield at about 186 GJ per hectare, similar to the energy crops common in northern Europe. But world primary energy use was about 592 EJ in 2024. At 186 GJ/ha, supplying that from hemp would take roughly 3.2 billion hectares, about twice the world’s entire cropland of around 1.6 billion hectares. That is gross heat in raw biomass, before the large losses in drying, pyrolysis or conversion to methanol. Even a modest share collides with food production. This is the food-versus-fuel problem that first-generation biofuels ran into, and hemp does not escape it.
Oil per hectare is weaker still. Recent Australian variety trials (2022–23) recorded hemp grain yields of roughly 1–2.7 t/ha and seed oil contents of 7% to about 29%. Even at the top of both ranges that is well under 1,000 L of oil per hectare; typical results work out to a few hundred litres. Hemp is below rapeseed and far below oil palm:
| Crop | Approx. oil yield (L/ha per year) |
|---|---|
| Hemp seed | a few hundred; under 1,000 even in the best case (calculated from Australian trial data) |
| Rapeseed (canola) | ~1,190 (widely cited figure) |
| Oil palm | ~5,950 (widely cited figure) |
Where the world actually went. The technologies that have displaced fossil fuel in the decades since are photovoltaics, wind and batteries — direct conversion, not combustion of biomass. Growing a crop, harvesting it, processing it and burning it is an inefficient way to capture solar energy compared with a panel that does it directly. Diesel’s own instinct — power from the heat of the sun — turned out to be right in a way he could not have anticipated, and it was not agricultural.
4. Where Hemp Oil Does Compete
Not as a fuel. As a material and a food, and the case there is solid.
Food. Hemp seed offers complete protein, an omega-6 to omega-3 ratio of 3:1 to 5:1, and roughly 1–4 g of gamma-linolenic acid per 100 g of oil depending on cultivar. Food is a much higher-value use of an oilseed than fuel, and always will be.
Industrial oil. Hemp seed oil dries to a hard film and has a long history in paints, varnishes and wood finishes — a use that does not require it to beat petroleum on energy content.
Cosmetics and personal care, where the fatty acid profile and price point work.
The pattern is consistent: hemp’s real modern opportunities are in specific applications where its properties matter — nutrition, insulation, moisture buffering, durable fibre — not in bulk commodity replacement of something cheaper.
5. Why It Is Worth Being Strict About This
Because the energy claim is the one most likely to be checked by someone who knows what they are talking about, and the one most likely to lose the argument.
An investor, an engineer or an agricultural economist encountering “hemp can replace fossil fuels” will discount everything else the speaker says. Meanwhile the verified case for hemp — the nutritional data, the hempcrete thermal and moisture figures, the fibre properties, the regulatory framework — is genuinely strong and genuinely commercial.
Overclaiming on energy costs more than it gains, and it costs it with exactly the audience a hemp business needs.
6. In Thailand
Thailand already runs a vegetable-oil diesel programme, and it runs on palm oil. Standard B7 diesel contains 7% palm-based biodiesel. B10 was withdrawn from sale in May 2024, the blend has since been adjusted between B5 and B7 as palm prices move, and B20 is offered mainly for trucks. Oil palm gives roughly ten times or more the oil per hectare that hemp seed does (see the table above), so hemp has no realistic place in Thai biodiesel. For a Thai grower the useful questions are food, fibre and materials, not fuel.
Hemp seed and seed oil are food and industrial materials, sitting outside the controlled-herb framework that governs cannabis flower. Flower is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568, issued 26 June 2025, and may be dispensed only on prescription form PT 33. Extracts containing more than 0.2% THC by weight remain Category 5 narcotics under the Ministry of Public Health notification specifying Category 5 narcotics (B.E. 2565, in force since 9 June 2022).
Licensing for hemp cultivation is less clear-cut. Since the 2022 delisting, growing hemp has generally not needed a narcotics licence, but growers have been expected to register through the Thai FDA’s Plookganja system. The two Ministerial Regulations B.E. 2569 then tightened licensing for cannabis/hemp extracts and controlled-herb businesses in 2026. The Cannabis Control Act is still a draft: Cabinet approved it on 22 September 2026 and sent it to the House, and it would bring in a new regime. Check current requirements with the Thai FDA before planting commercially. Food products also fall under Thai FDA food rules.
If anyone in the region is pressing hemp seed oil commercially: what is the yield per hectare you actually get, and what does the press cake sell for? Those two numbers determine whether any of this is a business, and neither appears in a single hemp advocacy book.
This article is part of the Asiannabis Community educational series on hemp and industrial cannabis. It concerns industrial hemp seed oil, not cannabis flower, and is general information rather than technical or legal advice.