"HOBC" simply means high octane petrol, which could be any number from 95RON to 99RON in Pakistan. It is simply the octane value of fuel and nothing else.
Euro 1,2,3,4,5,6 on the other hand are fuel emission standards adopted by the 28 member States of the European Union in order to protect the environment and human health by limiting the content of harmful substances in all crude oil based fuel. It essentially dictates how much of MMT, NOx, CO, HC and particulate matter a vehicle's exhaust system is allowed to emit per kilometre.
The higher or newer the Euro standard, the more stringent the emission rules.
When we say Euro5 fuel, what we mean is basically fuel that contains such an amount of these hazardous substances that when it is burned in a euro5 level catalytic converter equipped car it won't exceed the specified pollutant threshold. However, since a higher euro standard fuel contains less pollutant, even if it is run in a euro 2 or 4 car, the pollutant production would be much less and this would be beneficial for our health, environment and the vehicle as well.
Every country has its own emission standards. U.S. has EPA guidelines, Japan has its own, India has BS 1 to 6 standards which are pretty much replicas of euro standards which is why Euro6 and BS6 words are frequently used in place of each other. Pakistan has no standards, and no guidelines whatsoever, so we have blatantly copied the euro standards as well and didn't even change the name.
Also keep in mind in a euro 2 standard fuel, since the MMT threshold is much higher, oil refineries can easily just simply add more MMT to lets say 87RON -what they may actually be producing - and simply raise the RON value to 95 or whatever desired. This would bypass the regulations but at the same time make the fuel more harmful. OTOH, for euro5 HOBC they can't just add more MMT as this would exceed the threshold limit so they have to actually produce 95RON or higher fuel at the refinery distillation level. Which therefore, requires them to invest millions to upgrade their existing obsolete setup.
