Renault will supply Red Bull until 2018, and will also reunite with Toro Rosso for the next two seasons.
The deal comes as no surprise given the improved form of the French engine and the ongoing lack of an opportunity for Red Bull to move elsewhere.
After a year with Ferrari power STR will return to Renault, ensuring that once again there can be closer co-operation between the two teams. Both teams will have the right to badge the engine.
Christian Horner said: “We are delighted to extend our partnership which has proved very successful over time. After the reconstruction that Renault has undertaken, clear progress has been made which has made it logical to continue with the TAG Heuer badged engine.”
Adam Cooper's F1 Blog 
In Red Bulls case, isn’t it more of an obligation to badge the engine?