Answer
Under the Family Code, for a marriage celebrated on or after 3 August 1988 without a marriage settlement (prenuptial agreement), the default property regime is the Absolute Community of Property. Spouses may instead choose, in a marriage settlement executed before the marriage, the conjugal partnership of gains, complete separation of property, or any other regime not contrary to law (Articles 74 and 75).
For a marriage celebrated before 3 August 1988 under the Civil Code without a settlement, the default regime is the Conjugal Partnership of Gains, and the Family Code did not automatically convert those regimes to absolute community. A marriage settlement must be in writing, executed before the marriage, and registered in the local civil registry and the registries of property to bind third persons; it generally cannot be modified after the marriage except by a judicial decree of separation of property.