Del. Code tit. 18 § 1306
An insurer may invest in bonds or other evidences of indebtedness, not in default as to principal or interest, which are valid and legally authorized obligations issued, assumed or guaranteed by the United States or by any state thereof, or by Canada or any of the provinces thereof, or by any county, city town, village, municipality or district therein or by any political subdivision thereof or by a public instrumentality of 1 or more of the foregoing, and in any such obligations issued, assumed or guaranteed by the federal government of Mexico, if, by statutory or other legal requirements applicable thereto, such obligations are payable, as to both principal and interest, from (1) taxes levied or required to be levied upon all taxable property or all taxable income within the jurisdiction of such governmental unit, or from (2) adequate special revenues pledged or otherwise appropriated or by law required to be provided for the purpose of such payment; but not including any obligation payable solely out of special assessments on properties benefited by local improvements, unless adequate security is evidenced by the ratio of assessment to the value of the property or the obligation is additionally secured by an adequate guaranty fund required by law.
18 Del. C. § 1306