(a) In the event that a Federal estate tax is payable to the Federal Government on the transfer of the taxable estate of a decedent who was a resident of this Commonwealth at the time of his death, and the inheritance tax, if any, actually paid to the Commonwealth by reason of the death of the decedent (disregarding interest or the amount of any discount allowed under section 2142)¹ is less than the maximum credit for State death taxes allowable under section 2011 of the Internal Revenue Code of 1986 (Public Law 99-514, 26 U.S.C. § 2011), a tax equal to the difference is imposed. If a resident decedent owned or had an interest in real property or tangible personal property having a situs in another state, the tax so imposed shall be reduced by the greater of:

(b) In the event that a Federal estate tax is payable to the Federal Government on the transfer of the taxable estate of a decedent who was not a resident of this Commonwealth at the time of his death but who owned or had an interest in real property or tangible personal property having a situs in this Commonwealth, a tax is imposed in an amount computed by multiplying the maximum credit for State death taxes allowable under section 2011 of the Internal Revenue Code of 1986 (26 U.S.C. § 2011) by a fraction, the numerator of which is the value of the real property and tangible personal property to the extent included in the decedent's gross estate for Federal estate tax purposes having a situs in this Commonwealth and the denominator of which is the value of the decedent's gross estate for Federal estate tax purposes, and deducting from that amount the inheritance tax, if any, actually paid to the Commonwealth (disregarding interest or the amount of any discount allowed under section 2142).

(c) When an inheritance tax is imposed after an estate tax imposed under subsection (a) or (b) has been paid, the estate tax paid shall be credited against any inheritance tax later imposed.