UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

Report of Foreign Private Issuer
Pursuant to Rule 13a-16 or 15d-16 of the

Securities Exchange Act of 1934

For the month of May, 2026

Commission File Number 1-15106

PETRÓLEO BRASILEIRO S.A. – PETROBRAS

(Exact name of registrant as specified in its charter)

Brazilian Petroleum Corporation – PETROBRAS

(Translation of Registrant's name into English)

Avenida Henrique Valadares, 28 – 9th floor 
20231-030 – Rio de Janeiro, RJ
Federative Republic of Brazil

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover Form 20-F or Form 40-F. 

Form 20-F ___X___ Form 40-F _______

Indicate by check mark whether the registrant by furnishing the information contained in this Form is also thereby furnishing the information to the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934.

Yes _______ No___X____

1st Quarter 2026 Cash Basis ― TAXREPORT

INTERNA \ Força de Trabalho Gov. Take Municipalities States Federal RELATÓRIO FISCAL – 1° Trimestre de 2025 FEDERAL + GOV TAKE R$ 42.1 billion STATES R$ 29.6 billion MUNICIPALITIES R$ 0.7 billion R$ 72.4 billionPAID IN THE 1st QUARTER OF 2026 PetrobrasreportedaR$72.4billioncontributionforthegovernmentinthefirstquarterof2026.ThisamountincludesR$49.4billionintaxesduetoitsownoperations,R$14.8billioninGovernmentTake(Gov.Take),andR$8.2billionintaxeswithheldfromthirdparties. Inthefirstquarter,PetrobraspaidR$27.3billioninfederaltaxes,which,whencombinedwiththeR$14.8billioninGovernmentTake,totaledR$42.1billionallocatedtothefederalgovernment.Partofthisisdistributedtostatesandmunicipalitiesinaccordancewithcurrentlegislation.Thisfigurerepresentsapproximately5.4%oftotalfederaltaxrevenues.Comparedtothesameperiodofthepreviousyear,federalcontributionsincreasedby8%. Intermsofstatetaxpayments,PetrobrasdisbursedR$29.6billioninthefirstquarterof2026,representingapproximately12.3%ofthetotalcollectedbystates.Thiscorrespondstoa13.4%increasecomparedtothefirstquarterof2025,drivenbyhigheradremICMSratesonfuels(gasoline,dieselandLPG),effectiveasofJanuary1,2026,aswellasbytheincreaseintheethanolblendingasolinefrom27%to30%. MunicipaltaxesamountedtoapproximatelyR$0.7billionintheperiod,representingan18.3%increasecomparedtothesameperiodofthepreviousyear.Thisincreasereflectsservicecontractingactivitiesintheoilandnaturalgasexplorationandproductionsegment,whicharesubjecttoISS-STincidenceandwithholding.TheamountpaidtomunicipalitiesisprimarilydistributedamongISS-ST(taxeswithheldfromthirdparties),Petrobras’ownISS,andIPTU(UrbanPropertyTax). ThisTaxReportdetailsthecashoutflowsmadebyPetrobraswiththepaymentoftaxesandgovernmenttakeinthefirstquarterof2026.TheinformationfollowsthecashbasismethodandshouldbereadalongwiththeTaxReportforthefourthquarterof2025,onwhichthecomplianceaspectsandtaxriskmanagementoftheCompanyarepresented,aswellasthetaxpolicy,withitsprinciplesandguidelines,amongotherinformationaboutourroleasoneofthelargesttaxpayersintheBrazilianeconomy. TAX REPORT – 1st Quarter 2026 Cash Basis 1Q26 R$ 72.4, R$ 29.6 InMarch2026,ProvisionalMeasureNo.1,340wasenacted,establishingtheincidenceoftheExportTax(IE),effectiveasofMarch12,2026,onexportsofcrudepetroleumoiloroilfrombituminousminerals,aswellasdieselfuel.InMarch2026,anamountofR$5.5millionwascollectedasexporttax. Note:TaxpaymentsandGovernmentTakedatapresentedinthisreportiscalculatedonacashbasis,whichdiffersfromthefiguresdisclosedintheStatementofValueAdded(DVA),includedintheCompany’sFinancialStatementsandpreparedonanaccrualbasis. Comparison of Payment of the 1st Quarter(R$ Billion) 1Q25 1Q24 1Q23 1Q22 R$ 26.1 R$ 24.6 R$ 18.8 R$ 25.3 R$ 27.3 R$ 0.7 R$ 14.8 R$ 22.6 R$ 0.6 R$ 16.3 R$ 65.7, R$ 27.0 R$ 0.5 R$ 16.1 R$ 68.2, R$ 27.1 R$ .,4 R$ 16.3 R$ 62.6, R$ 21.3 R$ 0.4 R$ 22.9 R$ 69.9, TOTAL

INTERNA \ Força de Trabalho Collection History for the 1st Quarter(R$ Billion) Collection History of the Last 4 Quarters (R$ Billion) The charts below present the distribution of taxes paid by Petrobras, segmented by each tax nature. TAX REPORT – 1st Quarter 2026 Cash Basis Inthefirstquarterof2026,PetrobraspaidR$14.8billionasGovernmentTake,consistingofR$9.7billioninroyalties,R$4.2billioninSpecialParticipation,R$0.7billioninsignaturebonuses,andapproximatelyR$0.2billioninareaoccupationorretentionfees.Whencomparedtothesameperiodof2025,a9%decreaseisobserved,reflectinglowerpaymentsofSpecialParticipation. Inthelastfourquarters,PetrobrascontributedR$284.3billiontopublictreasuryastaxesandGovernmentTake. GOVERNMENT TAKE TAXES WITHHELD FROM THIRD PARTIES Royalties, special participation, signature bonuses, and payment for the occupation or retention of the área. Tax Responsible Taxes from our own operations COMPANY’S TAXES 2Q25 3Q25 4Q25 1Q26 27.5 22.9 29.7 29.6 30.5 66.2 68.0 77.7 72.4 25.2 22.6 0.4 0,5 0.7 15.4 15.1 21.7 Municipalities Federal States Total Gov. Take LEGENDA 0.4 27.3 14.8 1Q22 1Q25 25.3 27.0 18.8 21.3 62.6 0,5 69.9 16.3 22.9 29.6 68.2 65.7 72.4 1Q23 1Q24 1Q26 27.1 24.6 16.1 26.1 22.6 16.3 27.3 14.8 0.4 0.4 0.5 0.6 0.7

INTERNA \ Força de Trabalho Petrobras plays a relevant role in ICMS tax contribution, both as a taxpayer, due to its own operations, such as in the case of the monophase ICMS, and as a substitute taxpayer in transactions carried out by third parties. In 20 Brazilian states, Petrobras accounts for more than 10% of total ICMS payments, reinforcing the Company’simportance to the country. ThetablebelowhighlightsPetrobras’relevanceinthecontributionsoftaxesandGovernmentTakeallocatedtotheBrazilianstates.ThisanalysisisbasedoninformationdisclosedontheANPTransparencyPortal. TAX REPORT – 1st Quarter 2026 Cash Basis ICMS (R$ Million) GOVERNMENT TAKE(R$ Million) TOTAL (R$ Million) STATE Font: Portal of Transparency of each State TOTAL 29.6 4.2 33.8 3.6 0.1 - - - - - 0.02 0.4 - - - - - - - 0.1 - 0.0004 - - 0.02 - - - - - 7.3 6.1 3.8 2.0 1.9 1.9 1.8 1.7 1.3 1.2 0.8 0.6 0.4 0.4 0.3 0.3 0.3 0.3 0.3 0.3 0.2 0.2 0.1 0.1 0.1 0.1 0.03 Rio de Janeiro São Paulo Minas Gerais Mato Grosso Rio Grande do Sul Santa Catarina Goiás Paraná Espírito Santo Mato Grosso do Sul Pará Ceará Distrito Federal Paraíba Alagoas Tocantins Amazonas Piauí Rio Grande do Norte Rondônia Pernambuco Bahia Maranhão Sergipe Amapá Acre Roraima 3.7 6.0 3.8 2.0 1.9 1.9 1.8 1.7 1.0 1.2 0.8 0.6 0.4 0.4 0.3 0.3 0.2 0.3 0.3 0.3 0.2 0.1 0.1 0.1 0.1 0.1 0.03

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

Date: May 18, 2026

PETRÓLEO BRASILEIRO S.A–PETROBRAS

By: /s/ Fernando Sabbi Melgarejo

______________________________

Fernando Sabbi Melgarejo

Chief Financial Officer and Investor Relations Officer