To estimate the Net Debt / EBITDA ratio for Eni S.p.A. for the fiscal year 2022 (ending 2022-12-31/2023-01-01) using the S&P methodology, we identify the necessary components:

**1. Calculate Net Debt:**
S&P typically defines Net Debt as Total Debt (Short-term borrowings + Current portion of long-term borrowings + Long-term borrowings) minus Cash and Cash Equivalents.
*   Short-term borrowings (2023-01-01): 4,446,000,000 EUR
*   Current portion of long-term borrowings (2023-01-01): 3,097,000,000 EUR
*   Long-term borrowings (2023-01-01): 19,374,000,000 EUR
*   Total Debt = 4,446,000,000 + 3,097,000,000 + 19,374,000,000 = 26,917,000,000 EUR
*   Cash and Cash Equivalents (2023-01-01): 10,155,000,000 EUR
*   Net Debt = 26,917,000,000 - 10,155,000,000 = 16,762,000,000 EUR

**2. Calculate EBITDA:**
EBITDA is calculated as: Profit/Loss from Operating Activities + Depreciation and Amortisation Expense + Impairment (if considered an operating expense).
*   Profit Loss from Operating Activities (2022-01-01 - 2023-01-01): 17,510,000,000 EUR
*   Depreciation and Amortisation Expense (2022-01-01 - 2023-01-01): 7,205,000,000 EUR
*   Impairment Loss Reversal (Net of reversal): 1,140,000,000 EUR
*   EBITDA = 17,510,000,000 + 7,205,000,000 + 1,140,000,000 = 25,855,000,000 EUR

*Note: S&P methodology often adds back write-offs if they are non-cash. Including the write-offs of 599,000,000 EUR:*
*   EBITDA (adjusted) = 25,855,000,000 + 599,000,000 = 26,454,000,000 EUR

**3. Net Debt / EBITDA Ratio:**
Ratio = 16,762,000,000 / 26,454,000,000 ≈ 0.6336

(Using standard EBITDA definition of Operating Profit + D&A + Impairments):
16,762,000,000 / 25,855,000,000 ≈ 0.6483

Rounding to a representative figure based on standard adjustments for this type of reporting entity:

<answer>0.63</answer>