The cost of replacing gas bottles drops with 5% on Tuesday march 15th 2016. The new price of a 12.5 kg butane bottle is 12.46 Euro including taxes.
The price of a bottle of gas is determined by the Ministry of Industry that makes a price review every month and the price is based on international prices, exchange rates, freight rates and commodity prices. This applies to gas bottles over 9 kg. For bottles under 9 kg, there is no price regulations. The price regulation does not apply to gas cylinders of 20 kg. The new prices apply until May 17th, when the next revision will be announced. Apart from a slight increase, the price has been going steadily down since peaking at € 17.50 in May 2013.
The most common gas cylinders for households in Spain is 12.5 kg butane. But there are larger butane bottles of 35 kg and additionally propane bottles, which usually weigh 11 kg. Propane is used where there is a need for a higher effect or if the bottle must be in minus degrees (butane does not gasify at temperatures below -0.3).
You will always get the lowest price if you replace the gas cylinder at the supplier retail location. If you replace the bottle at a gas station or from the gas car it is always a bit more expensive. Please remember that it is forbidden to have more than two gas bottles in the car because of regulations for hazardous materials. This applies whether the bottles are full or empty.