Singapore celebrated the full reopening of with Malaysia last week, after land crossings closed two years ago due to . But the festive mood between the Southeast Asian neighbors has been dampened by of coming from Singapore to pump in Malaysia. It looks like for cheaper gas isn’t just a thing U.S. drivers do.

Some in Singapore have tried to save money by pumping lower grade gas at stations in Malaysia, Bloomberg . That gas is strictly for residents since 95 octane is subsidized by the Malaysian government — for Malaysian drivers. In fact, the sale of 95 octane to drivers in foreign-registered cars was banned in 2010, per the . So, selling the subsidized gas is a serious offense and carries serious fines. From :

The Johor division of Malaysia’s said it will step up enforcement against operators caught selling the fuel to foreign-registered cars, with companies liable for of up to 2 million ringgit ($474,400). Former Prime Minister Najib Razak also highlighted the issue in a , calling for increased monitoring of such sales.

Of course, that doesn’t mean Singaporean drivers are banned from pumping any gas in Malaysia. The more expensive and higher grade 97 octane is perfectly OK to pump in foreign cars; so is diesel. One other quirk — which would probably ruin my day if I was driving a — is that 97-RON comes out of green nozzles, while 95-RON comes from the yellow ones. Presumably, the colors help station attendants keep an eye on who’s pumping the cheaper gas.

But now, it’s not just station employees that are watching. The Malaysian government is sending officials to monitor stations along the border. As of this week, the says 95 octane costs (in USD) about $1.85 per gallon, compared to 97 octane at $3.52 per gallon. That’s quite a jump, but, again, it’s because the lower grade carries subsidies. Per :

Malaysia previously banned the sale of 95-RON gasoline to cars not registered locally because that grade of petrol is subsidized for residents. Singapore currently that [fuel] grade at more than four times what it costs in . Consumers’ desire for cheaper petrol comes as global oil prices surge. Singapore earlier made it mandatory for all locally-registered vehicles to have at least of their fuel tanks filled before driving out of the country.

So for those of you planning on going across the Causeway, just make sure you pumped at least three-quarters full before heading into Malaysia. And when you’re there, remember to use the green pumps.