He has been a full international referee for FIFA since 2001.
He was selected as a referee for the 2007 FIFA Under-20 World Cup in Canada, where he refereed the matches between the United States and South Korea on June 30, 2007, New Zealand and Gambia on July 5, 2007, and Austria and Chile on July 8, 2007. Aguilar was selected as a reserve official for the 2010 FIFA World Cup. Therefore, he did not officiate in any matches during the tournament except as a 4th official.
Also in 2011, he was selected for the 2011 CONCACAF Gold Cup including the Final at the Rose Bowl Stadium in Pasadena, California. On January 14, 2014, the FIFA Referees Committee appointed Aguilar as one of the referees to officiate at the 2014 World Cup in Brazil. He was once again selected to referee matches at the 2015 CONCACAF Gold Cup, and for the third Gold Cup in a row, he was selected to referee the final match. On January 22, 2016, he was named CONCACAF 2015 Male Referee of the Year.
Aguilar has officiated in various international tournaments at both the club and international level, such as:
- 11 Salvadoran League finals
- International Friendlies
- 2007 CONCACAF Gold Cup
- 2007 FIFA U-20 World Cup
- 2007 FIFA U-17 World Cup
- 2007 North American SuperLiga
- 2009 CONCACAF Gold Cup
- 2010 FIFA World Cup qualification (CONCACAF)
- 2010 FIFA World Cup
- 2011 CONCACAF Gold Cup (including the Final)
- 2011 CONCACAF Champions League Final
- 2011 FIFA Club World Cup
- 2013 FIFA Confederations Cup
- 2013 CONCACAF Gold Cup (including the Final)
- 2014 FIFA World Cup qualification (CONCACAF)
- 2014 FIFA World Cup
- 2015 CONCACAF Gold Cup (including the Final)
- 2015 CONCACAF Cup
- 2016 Copa América Centenario
- List of prospective 2010 FIFA World Cup referees
- Referees & Assistant referees for the 2014 FIFA World Cup
- "Javier Hernandez and Carli Lloyd Named 2015 CONCACAF Players of the Year". concacaf.com. January 22, 2016. Retrieved 27 February 2016.