Article 54 establishes the 'wholly and exclusively' principle for tax deductions in Oman. To be deductible from gross income, an expense must be actually incurred during the tax year and used entirely for the purpose of producing that income. If an expense is only partially related to income production, only the relevant portion is deductible. Crucially, any expenses related to the production of tax-exempt income are strictly non-deductible. This fundamental rule prevents taxpayers from reducing their taxable base through personal or non-business expenditures or costs associated with non-taxed revenue streams.