Hi everyone, I haven't posted on Briskoda meaningfully in a long time. I used to be very active in the Superb sub-forums over the ~15 years I've had Škodas. I've read with interest the many MPG threads on here over those years, and always wondered about my own cars, too. So, I decided to actually put the matter to bed. In my previous Superb (2.0 TSI 220ps DSG) I felt 99 RON gave a power and MPG edge over 95 RON fuel. The BMW X2 20i xDrive that followed it, definitely so! When it came to my 2024 Mk I Kodiaq 1.5 TSI EVO ACT DPCA 150ps DSG SE-L Executive (7 seats, 19" wheels), though? I wasn't so sure. The car 'felt' sharper, but MPG didn't seem much different. I'd never actually tested it, just gone off 'feel' and transient leg/tank MPGs. I decided to log every fill and every single journey(!) over 11 tanks of fuel and 4,000 plus driven miles. I have tested 95 RON, 97 RON, 98 RON (blended) and 99 RON — as well as various additives like Miller's Petrol Power ECOMAX (no difference), Redex Petrol System Cleaner (smoother drive, mild MPG uplift), Archoil AR6900-P Max (large MPG uplift, dull/flat drive), Oilsyn Petrol Power DNA (strong PEA detergent, lubricious — raised MPG floors but introduced a lot of ECU adaptation and 'unsettled' feel, somewhat capped MPG ceilings). Then, finally, I came across Oilsyn Hybrogen Road. Hybrogen is an interesting one, and as soon as I read about it I knew I just had to test it. It is the only additive I've come across that clearly advertises a positive MPG gain. That is, dosed at only 1:3000 (1ml per 3 litres of fuel) it claims to increase torque, power and MPG above and beyond an identical factory-clean engine when used in either petrol or diesel road fuels. Not 'cleans back to factory and restores lost MPG', but actually physically raises MPG, period. It's not a detergent (directly), nor does it affect octane or lubricity. It's a nano-colloid which basically acts as a dispersant, surfactant and combustion modifier. It removes water from fuel (eg ethanol blends), cleans the fuel system, and — most importantly — aggressively homogenises the hydrocarbons in fuel (petrol or diesel) for a consistent and clean burn. That, they say, results in a higher MPG while increasing power and torque across the whole area under the curve. Sounds like woo?... Long story short, my average MPGs (mostly short, urban journeys from cold tested across pair-matched routes and drive cycles) ended up at: Fuel mix Tank average MPG Uplift over baseline Unadditised 95 RON ~30.0 - Unadditised 99 RON ~30 - 95 RON + Hybrogen 37.4 24.67 % 99 RON + Hybrogen 34.5 15 % Hybrogen long term average 36.0 20 % I should add that the 95 RON + Hybrogen tank includes a return trip from Devon to Liverpool. As such, the 99 RON + Hybrogen tank (~35 mpg) and its 15% uplift is more representative overall of the realistic tank average of this fuel/additive mix day-to-day. For example, if you read the full dataset, tank 7 (95 RON + Hybrogen) closed at 35.2 mpg and didn't include a longer motorway leg. However, the long term average (30 -> 36 MPG) includes a fully representative mix of driving in both cases, and the overall average increase of 20% over unadditised baseline stands validated. Fuel mix Urban MPG Pence per mile Unadditised 99 RON ~30 24.0 Unadditised 95 RON ~30 22.7 99 RON + Hybrogen 34.5 20.8 95 RON + Hybrogen 37.4 17.9 I tested by running a tank of X mix first, then took the uplift measurement from the second subsequent tank of the same octane/additive mix, to allow time for ECU adaptation and fuel trims to settle etc. Interestingly, withdrawing Hybrogen (diluting it out of efficacy) caused MPG to regress back to the same ~30 MPG baseline tank average, restoring back to mid-30s MPG once reintroduced on subsequent tanks. I also ran paired matched-route analysis and various other statistical tests on the (large!) dataset, and the winning fuel for this engine in my mixed driving cycle is unequivocally 95 RON + Hybrogen. There was no benefit in 97–99 RON fuels at all (this engine is not knock-limited in regular driving), and in fact they were harder to extract good economy from because the higher octane shortened the torque response vs throttle travel, resulting in a 'hair trigger' and more transient fuelling events. While the numbers might seem outlandishly large, please remember that (1) independent testing — including university testing — on the Oilsyn website shows similar numbers across various engines and regimes, and (2) my uplift came unambiguously from both the additive's direct effect on fuel, and the secondary effects such as the broader torque curve allowing gentler throttle at cruising speed, prolonged ACT engagement etc. Combined, the uplift is what you see above, and it's repeatable. The full (mildly anonymised) dataset and all my notes throughout can be read on Github as a Gist if you're interested. GistŠkoda Kodiaq 1.5 TSI fuel economy: Oilsyn Hybrogen additi...Škoda Kodiaq 1.5 TSI fuel economy: Oilsyn Hybrogen additive test - fuel-test-anonymised.md TL,DR: If your car says Min. 95 RON then — unless you're lapping the Nurburgring at three figures and ten tenths — just save money and use 95 RON (and Hybrogen!). No matter the scenario, from urban short hops from cold, through fully-loaded fast ~300 mile motorway runs up Devonshire hills with 7 people on board while pulling a roof box and hundreds of KG of luggage, 95 RON worked out both most economical (MPG) and cheapest at the pump. Please note I made no money from this testing, I wasn't paid for it, I'm unrelated to Oilsyn or any other fuel additive seller, and I'm just a long-term member here who decided to answer my own question as best I could. This is what resulted from that! Take from it what you will. Personally, I'd never go without using Hybrogen again. Not only does its modest cost (~1 ppl extra) pay for itself and then some, but the annual savings as detailed in the full report are huge (up to ~£500/year at 10,000 miles of mixed driving). Full fuel costs, pence per mile and other metrics are included in the full report/dataset if you're interested. Cheers!