The 'silver goal' ruling brought in by UEFA will make its debut at the UEFA Cup final between Celtic and Porto at the Estadio Olimpico in Seville on May 21.
The system, which will also be used at the Champions League final in Manchester on May 28, has been launched by European football's governing body to replace the sudden-death golden goal system that has been in force for the past few seasons.
Under the 'silver goal' ruling, if the Champions League and UEFA Cup finals end in a draw after 90 minutes, a first 15 minutes of extra-time will be played. If one team is in the lead at the end of the 15 minutes, that team will be declared the winners of the match.
If the two teams are still level after 15 minutes of extra-time, a second 15-minute period will be played.
If the result remains deadlocked at the end of the second period of extra-time, a penalty shoot-out will determine the winners.
The move has come about following criticism of the effects of the golden goal ruling, such as that it put too much pressure on referees, prompted teams to play negative football and that the sudden end to a match can cause safety and security concerns.
"We believe that this will be good for clubs, players and fans," UEFA communications and public affairs director Mike Lee said on the organisation's official website, www.uefa.com.
"We have addressed the problems created by the golden goal which many in the game have identified. The new system will encourage positive football in the extra-time period, and produce a sensible and fairer ending to a game."
The golden goal rule previously settled the destiny of the Euro '96 and Euro 2000 titles.
Germany won in sudden-death fashion during extra-time in the Euro '96 final against the Czech Republic in England, and France triumphed in a similar manner against Italy in Holland three years ago.