9. Commitments and Contingencies

Operating Leases

We lease facilities space and equipment under operating lease arrangements that have terms expiring at various dates through 2020. Certain lease arrangements include renewal options and escalation clauses. In addition, various lease agreements to which we are party require that we comply with certain customary covenants throughout the term of these leases. If we are unable to comply with these covenants and cannot reach a satisfactory resolution in the event of noncompliance, these agreements could terminate.

Future minimum lease payments under non-cancelable operating leases are as follows (in thousands):

Year Ending December 31,

2014	$	3,285
2015		3,195
2016		3,043
2017		2,998
2018		2,343
Thereafter		365


	$	15,229

Total rent expense was $3.5 million, $3.6 million and $4.6 million for the years ended December 31, 2013, 2012 and 2011, respectively.

Milestone Payments

We are party to certain license agreements as described in Note 15—Assignment and License Agreements and acquisition agreements. Generally, these agreements require that we make milestone payments in cash upon the achievement of certain product development and commercialization goals and payments of royalties upon commercial sales.

Future milestone payments based on our estimates of the timing and probability of achieving milestones specified under these arrangements are as follows (in thousands):

Year Ending December 31,	(1)

2014	$	4,300
2015		1,450
2016		2,247
2017		6,668
2018		1,075
Thereafter		6,170


Total	$	21,910

(1): The amounts and timing of future milestone payments may vary depending on when related milestones will be attained, if at all.

Research Agreement

We maintain a research agreement with the University of Oxford (Oxford) to develop antiviral compounds. Research under this agreement is performed by Oxford Glycobiology Institute, which is headed by a member of our Board of Directors and our scientific advisory board. Under the terms of the agreement, we are required to fund related research activities and make milestone payments for the successful completion of clinical trials. We are also obligated to pay royalties to Oxford equal to a percentage of our net sales from any discoveries and products developed by Oxford. Milestone payments and royalties are subject to reduction depending upon third-party contributions to discoveries and/or third-party licenses necessary to develop products. In August 2010, the term of the research agreement was extended through September 2016. In connection with the extension of the term, we agreed to pay Oxford a total of $2.9 million (using the then-prevailing exchange rate) in sixty equal installments. As of December 31, 2013, approximately $1.7 million remains outstanding under this 2010 agreement. In addition, in December 2012, we amended our agreement with Oxford, under which we agreed to pay Oxford an additional $871,000 in the aggregate (using the exchange rate as of the amendment date) in thirty-six equal installments for additional work supporting the development of our virology platform which began in January 2013. As of December 31, 2013, approximately $594,000 remains outstanding under this 2012 amendment. During the years ended December 31, 2013, 2012 and 2011, we incurred approximately $890,000, $577,000 and $658,000, respectively, in expenses under the terms of the agreement.

From time to time, we may enter into other service agreements with Oxford relating to specific development activities that are outside the scope of our research agreement described above. We incurred expenses of approximately $55,000, $336,000 and $550,000 relating to these additional services during the years ended December 31, 2013, 2012 and 2011, respectively.