The quarterfinals of the 2015-16 Champions League soccer tournament take place in less than a week. Tickets for the annual event are pricey, but generating wide interest, even from outside the European continent, where the games are taking place.

The Champions League is widely considered the world's toughest club tournament. It runs from late summer to the following spring and features Europe's best teams, including Spain's FC Barcelona and Real Madrid, Germany's Bayern Munich and France's Paris St. Germain (PSG).

Ticketbis offers insight on the best-selling matchups, ticket prices and international sales.

The most intriguing matchup arguably pits Spanish rivals Barcelona and Atletico Madrid. Tickets to the two games between the teams are accounting for 58.6% of all Champions League purchases. Barcelona is perhaps the world's best-known soccer brand. The team includes high-priced, South American stars Lionel Messi, Luis Suarez and Neymar. The Argentinian Messi is the all-time leading scorer in the Spanish League. But Atletico Madrid counters with a stout defense and has made a habit recently of knocking off highly regarded teams.

Barcelona and Atletico will play a two-game series - one apiece at each other's home stadiums. If the teams each win one game, a tiebreaker based on total goals scored ais used to decide who will advance.

The average price of a ticket to watch the game at Barcelona's iconic Camp Nou is $300.60 with a get-in price of $164.50. The second leg at Madrid's Vicente Calderon currently averages a $242.50 ticket with a get-in price of $151.80.

The next most sought-after matchup is PSG vs. Great Britain's Manchester City with 26.1% of ticket purchases on the Ticketbis platform. The teams played to a draw the only time they met during the 2008-09 Champions League. PSG is the four-time defending Ligue 1 champion. Ligue 1 is the top French League.

This year, PSG clinched the title two months remaining in its schedule, a European record. It features the Brazilian defender David Luiz and the remarkable, Swedish striker, Zlatan Ibrahimovic.

Still, PSG is not the clear favorite against Manchester City, which has won two of the last English Premier League Championships. The English Premier League is considered the world's most challenging soccer league.

The average resale price for a ticket at Parc de Prince in Paris is $394.40 with a get-in price of $213.63. The second leg at Etihad Stadium in Manchester is less expensive with an average price of $240.80 and a get-in price of $166.70.

Real Madrid will be a heavy favorite against Germany's Wolfsburg, a surprise quarterfinalist. Wolfsburg has only played in Germany's top division since the late 1990s, while Madrid has won a record 10 Champions League titles and features Portugal's star striker Cristiano Ronaldo.

Bayern Munich will be the favorite in its series against the two-time, defending Portuguese league champion, Benfica. Munich is a five-time Champions League winner with its most recent title in 2013. Ticket sales to the Madrid-Wolfsburg and Munich-Benefica series have been less robust than for the other two series.

That said, according to Ticketbis, sales registered outside of the continent are at an all-time high, with significant interest coming from the U.S., Mexico, Brazil and Argentina. So far, 12.3% of sales for this year's Champions League quarterfinal matchups have been registered in the U.S., the highest they have been for any international soccer competition in Europe. That reflects rising interest in the U.S. for high-level European soccer.

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.