August 30, 2010

Exhibit 10.91

JPMorgan Chase Bank, National Association

P.O. Xxx 000

00 Xxxxxxxx Xxxxxxxxxx

Xxxxxx XX0X 0XX

Xxxxxxx

August 30, 2010

To: Gilead Sciences, Inc.

000 Xxxxxxxx Xxxxx

Xxxxxx Xxxx, Xxxxxxxxxx 00000

Attention:		Treasurer
Telephone No.:		(000) 000-0000
Facsimile No.:		(000) 000-0000

Re: Additional Call Option Transaction (2014)

1.        Reference is made to the letter agreement Re: Additional Call Option Transaction (2014) dated August 5, 2010 and entered into between into between JPMorgan Chase Bank, National Association, London Branch (“Dealer”) and Gilead Sciences, Inc. (“Counterparty”) (the “Confirmation”). Capitalized terms used herein but not defined herein shall have the meanings assigned to them in the Confirmation.

2.        Whereas the Confirmation defined the Free Convertibility Date as April 1, 2014, but Counterparty and Dealer wish to define the Free Convertibility Date as February 1, 2014;

3.        Now, therefore, each of Counterparty and Dealer do hereby agree that:

a.        the definition of the Free Convertibility Date in the Confirmation is hereby replaced in its entirety by February 1, 2014;

b.        (i) X.X. Xxxxxx Securities Inc., an affiliate of Dealer (“JPMSI”), has acted solely as agent and not as principal with respect to the Transaction and (ii) JPMSI has no obligation or liability, by way of guaranty, endorsement or otherwise, in any manner in respect of the Transaction (including, if applicable, in respect of the settlement thereof);

c.        each of Counterparty and Dealer will look solely to the other party (or any guarantor in respect thereof) for performance of such other party’s obligations under the Transaction; and

d.        this agreement may be signed in any number of counterparts, each of which shall be an original, with the same effect as if all of the signatures thereto and hereto were upon the same instrument.

[Signature Page to Follow]

Very truly yours,
X.X. Xxxxxx Securities Inc., as agent for JPMorgan Chase Bank, National Association
By:		/s/ Xxxxx X. Xxxx
Authorized Signatory
Name:		Xxxxx X. Xxxx Managing Director

Accepted and confirmed:

Gilead Sciences, Inc.

By:		/s/ Xxxxx X. Xxxxxxxx
Name:		Xxxxx X. Xxxxxxxx
Title:		Vice President and General Counsel