To determine the extent to which Naturgy Energy Group SA should utilize hybrid bonds, we must analyze its current capital structure, credit profile, and the specific constraints provided by S&P Global Ratings regarding equity credit for hybrid instruments.

**1. Calculate Current Capital Structure (as of 2023-01-01):**

First, we identify the relevant components from the balance sheet data provided:
*   **Total Equity:** 9,979,000,000 EUR
*   **Total Debt (Financial Liabilities):**
    *   Noncurrent Financial Liabilities: 13,999,000,000 EUR
    *   Current Financial Liabilities: 2,302,000,000 EUR
    *   *Total Debt* = 13,999 + 2,302 = 16,301,000,000 EUR

*Note: S&P's "Total Adjusted Capital" is generally defined as Total Debt + Total Equity. In some specific rating methodologies, adjustments are made for hybrids, but the base calculation starts here.*

*   **Total Adjusted Capital (Base):** 16,301,000,000 (Debt) + 9,979,000,000 (Equity) = 26,280,000,000 EUR.

**2. Analyze the S&P Global Ratings Constraint:**

The prompt states that S&P limits the equity credit on hybrids to a maximum of **15% of total adjusted capital**.
*   Hybrid bonds are debt instruments that can receive partial equity credit (typically 50% for strong issuers, less for weaker ones) if they meet specific criteria (perpetual, deferrable coupons, etc.).
*   The "equity credit" is the portion of the hybrid's value treated as equity for rating purposes.
*   The constraint is: $Equity Credit \le 15\% \times Total Adjusted Capital$.

Let $H$ be the amount of hybrid bonds issued.
Let $EC\%$ be the equity credit percentage assigned by S&P (usually 50% for investment-grade utilities like Naturgy, but can vary).
The equity credit amount is $H \times EC\%$.

The constraint becomes:
$H \times EC\% \le 0.15 \times (Debt + Equity + H_{adjustments})$

However, a more practical interpretation for "utilization relative to the cap" asks how much of the *available* hybrid capacity the company should use. Companies typically issue hybrids to optimize their Weighted Average Cost of Capital (WACC) and improve leverage ratios (by treating part of the debt as equity).

**3. Assess Naturgy's Credit Profile and Market Conditions:**

*   **Credit Rating Context:** Naturgy is an investment-grade utility. Utilities often have higher tolerance for leverage due to stable cash flows.
*   **Leverage Ratio:**
    *   Debt / (Debt + Equity) = 16,301 / 26,280 ≈ 62%.
    *   This is a moderate-to-high leverage ratio for a utility. Reducing reported leverage via hybrid equity credit is beneficial.
*   **Market Data (2022):**
    *   Interest rates rose significantly in 2022 (Swap curves moved from negative to ~1.7-1.9%).
    *   Corporate bond spreads widened (iBoxx EUR Non-Financial IG delta increased).
    *   Despite higher costs, hybrid bonds remain a key tool for utilities to bridge the gap between debt and equity.

**4. Determining the "Extent" of Utilization:**

The question asks for the extent of utilization *relative to the cap*. The options are 0%, 25%, 50%, 75%, 100%.

*   **0%:** Incorrect. Naturgy has existing hybrids or the capacity/need for them. Issuing 0% would ignore the capital structure optimization benefit.
*   **100%:** This would mean issuing hybrids up to the absolute maximum limit allowed by S&P (where the equity credit equals exactly 15% of total capital). While theoretically optimal for leverage reduction, it is rarely practical to hit the exact cap due to investor demand, cost considerations, and rating agency buffers. However, in the context of multiple-choice questions about "optimal" or "target" utilization relative to a regulatory/rating cap, companies often aim to maximize the benefit within the constraint.
*   **Standard Practice:** Investment-grade utilities typically target a hybrid component that maximizes the equity credit benefit without jeopardizing the rating. S&P's 15% cap is a *limit*. Most aggressive optimizers will aim to get close to this limit to maximize the equity treatment.
*   **Naturgy's Specific Situation:** Naturgy has actively managed its capital structure. In recent years, many European utilities have increased hybrid issuance. The "cap" is a hard ceiling. To answer "to what extent... relative to the cap", we look at whether they are under-utilizing, moderately utilizing, or fully utilizing the allowance.
*   Given the high leverage (62%) and the need to support the investment-grade rating, Naturgy has a strong incentive to utilize the hybrid instrument to its fullest allowable extent to lower its *adjusted* leverage. Therefore, the strategic target is typically to fill the bucket allowed by the rating agency.

However, let's look closer at the phrasing "utilize hybrid bonds relative to S&P Global Ratings' cap".
If the cap is 15% of capital, and the company issues hybrids such that the equity credit is 15% of capital, it is utilizing 100% of the *allowed capacity*.

Is there a reason to choose 50% or 75%?
Often, rating agencies apply a "notch" deduction if hybrids exceed a certain threshold, or the equity credit might be reduced if the volume is too high relative to tangible equity. But the prompt explicitly defines the cap: "limits the equity credit on hybrids to a maximum of 15% of total adjusted capital". This implies that up to this point, the treatment is standard. Beyond this, benefits might diminish or ratings suffer. Therefore, a rational actor seeking to optimize capital structure within rating constraints will aim to utilize **100%** of this specific allowance (the 15% bucket).

Let's double-check if Naturgy already has hybrids. The balance sheet shows "Noncurrent Financial Liabilities" and "Equity". It does not explicitly break out "Hybrid Bonds" in the provided line items, but "Other Noncurrent Financial Liabilities" is very small (1M EUR). However, "Noncontrolling Interests" is 2.4B EUR. Sometimes hybrids are classified elsewhere or the data provided is aggregated. Regardless, the question is prescriptive: "To what extent *should* this company utilize...".

Given the high interest rate environment (2022 data), issuing hybrids is more expensive than in 2020/2021. However, they are still cheaper than equity and improve leverage metrics. The "cap" represents the maximum efficiency point for rating purposes. Utilizing less than the cap (e.g., 50%) leaves "free" equity credit on the table, resulting in higher reported leverage than necessary. Utilizing more than the cap provides no additional equity credit benefit and increases cost. Therefore, the optimal theoretical utilization relative to the cap is 100%.

<answer>100%</answer>