Generally metrykal records in Ukraine can be located by time frame.
There is no prepayment at most Ukrainian Archives. In some archives, finding someone who is Spanish speaking can be a problem. It is best to communicate in Ukrainian. All answers will come to you in Ukrainian.
WHAT IS KEY IS KNOWING EXACT PLACE OF ORIGIN FOR YOUR IMMIGRANT/ANCESTOR. That information can be obtained by researching ship manifests or other even church records. Ukrainian-Argentinian metrykal records were quite detailed.
Immigrants frequently referred to their place of origin as the district
or regional center town for geographical reference, because their
own villages were small.
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Records older than 100 years are located in Historical Archives,
either in Lviv or Kyiv.
Records between 75-100 years old are at the oblast/regional Archives. Places like Vohlynia are complicated. This region has been divided into smaller oblasts. Some Greek Catholic records are in Lviv, some Orthodox records are in Lutsk.
I think records in what was Vohlyn oblast once, and the Zakarpatska oblast are the most difficult to locate.
Records under 75 years are located at the District Archives/RAHS.
These records fall under International Privacy Laws and a PRIVACY
RELEASE must be obtained by writing your nearest Ukrainian
Embassy or Consulate and requesting permission to make the
inquiry. I am not sure what the charges may be in Argentina.
The Embassy or Consulate will provide you with the individual
RAHS address.