2005 California Civil Code Sections 1605-1615 CHAPTER 5. CONSIDERATION

1605.  Any benefit conferred, or agreed to be conferred, upon the
promisor, by any other person, to which the promisor is not lawfully
entitled, or any prejudice suffered, or agreed to be suffered, by
such person, other than such as he is at the time of consent lawfully
bound to suffer, as an inducement to the promisor, is a good
consideration for a promise.
1606.  An existing legal obligation resting upon the promisor, or a
moral obligation originating in some benefit conferred upon the
promisor, or prejudice suffered by the promisee, is also a good
consideration for a promise, to an extent corresponding with the
extent of the obligation, but no further or otherwise.
1607.  The consideration of a contract must be lawful within the
meaning of Section 1667.
1608.  If any part of a single consideration for one or more
objects, or of several considerations for a single object, is
unlawful, the entire contract is void.
1609.  A consideration may be executed or executory, in whole or in
part. In so far as it is executory it is subject to the provisions of
Chapter IV of this Title.
1610.  When a consideration is executory, it is not indispensable
that the contract should specify its amount or the means of
ascertaining it.  It may be left to the decision of a third person,
or regulated by any specified standard.
1611.  When a contract does not determine the amount of the
consideration, nor the method by which it is to be ascertained, or
when it leaves the amount thereof to the discretion of an interested
party, the consideration must be so much money as the object of the
contract is reasonably worth.
1612.  Where a contract provides an exclusive method by which its
consideration is to be ascertained, which method is on its face
impossible of execution, the entire contract is void; but this
section shall not apply to the cases provided for in sections 1729
and 1730 of this code.
1613.  Where a contract provides an exclusive method by which its
consideration is to be ascertained, which method appears possible on
its face, but in fact is, or becomes, impossible of execution, such
provision only is void; but this section shall not apply to the cases
provided for in sections 1729 and 1730 of this code.
1614.  A written instrument is presumptive evidence of a
consideration.
1615.  The burden of showing a want of consideration sufficient to
support an instrument lies with the party seeking to invalidate or
avoid it.